MChem Master of Chemistry — Questions and Answers

Question 1: What is the glass transition temperature (Tg) and why is it important for polymer materials?

The melting point of the crystalline domains in a semi-crystalline polymer
The temperature below which an amorphous polymer transitions from rubbery to glassy behavior (Correct answer)
The temperature at which a crystalline polymer melts
The temperature at which a polymer begins to degrade

Correct answer: The temperature below which an amorphous polymer transitions from rubbery to glassy behavior

Tg marks the onset of large-scale segmental motion; below Tg, amorphous polymers are rigid and brittle, above Tg they are soft and rubbery.

Question 2: Which industrial process converts naphtha into high-octane aromatics and hydrogen using a platinum-rhenium catalyst?

Fluid catalytic cracking
Steam cracking
Hydrocracking
Catalytic reforming (platforming) (Correct answer)

Correct answer: Catalytic reforming (platforming)

Catalytic reforming (e.g., UOP Platforming) dehydrogenates and cyclizes naphtha over Pt-Re/Al2O3 to produce aromatics and H2.

Question 3: Which ICH guideline specifically addresses impurity thresholds and qualification requirements for drug substances?

ICH Q8
ICH Q6A
ICH Q3A (Correct answer)
ICH Q1A

Correct answer: ICH Q3A

ICH Q3A (Impurities in New Drug Substances) defines reporting, identification, and qualification thresholds for chemical impurities in APIs.

Question 4: What is the purpose of Ewald summation in periodic boundary condition simulations?

To efficiently compute long-range electrostatic interactions (Correct answer)
To correct for quantum tunneling effects
To integrate equations of motion more accurately
To sample configurational space faster

Correct answer: To efficiently compute long-range electrostatic interactions

Ewald summation splits the long-range Coulomb sum into rapidly converging real-space and reciprocal-space components for periodic systems.

Question 5: In sol-gel chemistry, what reaction converts metal alkoxide precursors into a metal oxide network?

Thermal decomposition at high temperature
Electrolytic oxidation of metal salts
Reduction followed by precipitation
Hydrolysis and condensation polymerization (Correct answer)

Correct answer: Hydrolysis and condensation polymerization

Metal alkoxides (e.g., TEOS for silica) undergo hydrolysis to form silanols, which then condense via Si–O–Si bond formation to build an amorphous oxide network.

Question 6: What does the BOD (Biochemical Oxygen Demand) measurement indicate about a water sample?

The amount of oxygen consumed by microorganisms to degrade organic matter (Correct answer)
The concentration of nitrate and phosphate nutrients
The total dissolved oxygen concentration
The pH buffering capacity of the water

Correct answer: The amount of oxygen consumed by microorganisms to degrade organic matter

BOD measures the oxygen consumed by microorganisms when decomposing organic matter in water over 5 days at 20°C, indicating organic pollution load.

Question 7: In transition state theory (Eyring theory), the rate constant is expressed as k = (k_BT/h)·K‡. The transmission coefficient κ is often set to 1, which assumes:

The reaction is barrierless
The pre-exponential factor equals k_BT/h
Every activated complex that reaches the transition state proceeds to products (Correct answer)
No quantum tunneling occurs

Correct answer: Every activated complex that reaches the transition state proceeds to products

κ = 1 assumes all transition state complexes proceed forward to products without recrossing the barrier.

Question 8: Which analytical technique is the gold standard for absolute stereochemical assignment in pharmaceutical compounds?

Circular dichroism spectroscopy
X-ray crystallography (Correct answer)
Optical rotation polarimetry
Chiral HPLC

Correct answer: X-ray crystallography

X-ray crystallography provides definitive absolute configuration by directly mapping atomic positions in space, including stereogenic centers.

Question 9: For an ideal gas undergoing a reversible adiabatic expansion, which relationship between pressure P and volume V holds (γ = C_p/C_v)?

PV^γ = constant (Correct answer)
P^γV = constant
P/V^γ = constant
PV = constant

Correct answer: PV^γ = constant

A reversible adiabatic (isentropic) process for an ideal gas obeys PV^γ = constant, derived from the first law with dq = 0.

Question 10: The Debye-Hückel limiting law for activity coefficients in dilute electrolyte solutions gives log γ± = −A|z₊z₋|√I, where I is the ionic strength. For a 1:1 electrolyte at concentration c, the ionic strength I equals:

2c
c²
c (Correct answer)
c/2

Correct answer: c

For a 1:1 electrolyte, I = ½Σcᵢzᵢ² = ½(c·1² + c·1²) = c.

Question 11: What structural feature of metal-organic frameworks (MOFs) gives them among the highest surface areas of any known materials?

Their highly porous crystalline structures built from metal nodes connected by organic linkers (Correct answer)
Their amorphous disordered arrangement of metal atoms
Their dense close-packed metal layers
Their multi-walled nanotube geometry

Correct answer: Their highly porous crystalline structures built from metal nodes connected by organic linkers

MOFs combine metal ion/cluster nodes with organic linker struts to form crystalline porous frameworks, achieving surface areas exceeding 7,000 m²/g in some materials.

Question 12: What is 'selectivity' in industrial heterogeneous catalysis, and how does it differ from 'conversion'?

Selectivity is the fraction of reacted feedstock forming the desired product; conversion is the fraction of feed that has reacted (Correct answer)
Selectivity measures catalyst lifetime; conversion measures throughput
They are interchangeable terms for overall process efficiency
Selectivity is the fraction of reactant consumed; conversion is the fraction forming desired product

Correct answer: Selectivity is the fraction of reacted feedstock forming the desired product; conversion is the fraction of feed that has reacted

Conversion = (moles reacted)/(moles fed); selectivity = (moles to desired product)/(moles reacted), so yield = conversion × selectivity.

Question 13: Which of the following best explains why aromatic compounds undergo electrophilic substitution rather than addition?

Aromatic rings cannot form sigma complexes with electrophiles
Addition products are thermodynamically more stable
Substitution restores the aromatic ring's stability after electrophile attack (Correct answer)
Electrophilic addition is kinetically too slow for benzene

Correct answer: Substitution restores the aromatic ring's stability after electrophile attack

After the electrophile forms a sigma complex (arenium ion), loss of a proton restores aromaticity, making substitution the thermodynamically favored pathway.

Question 14: In the Diels-Alder reaction, which diene conformation is required for the reaction to proceed?

anti-periplanar
s-trans
s-cis (Correct answer)
gauche

Correct answer: s-cis

The diene must adopt the s-cis conformation so that both terminal carbons can interact with the dienophile in a concerted [4+2] cycloaddition.

Question 15: The Butler-Volmer equation describes electrode kinetics. At large overpotentials η >> RT/F, the current simplifies to the Tafel equation. What does the Tafel slope b represent?

The rate of change of ln|i| with overpotential η (Correct answer)
The standard exchange current density
The equilibrium potential at zero current
The transfer coefficient α directly

Correct answer: The rate of change of ln|i| with overpotential η

The Tafel slope b = d(η)/d(log|i|) and equals 2.303RT/(αF), characterizing how current varies with applied overpotential.

Question 16: Prussian blue, Fe₄[Fe(CN)₆]₃, exhibits intense color due to which phenomenon?

d-d electronic transitions forbidden by the Laporte rule
Ligand-to-metal charge transfer (LMCT) from CN⁻ to iron
Intervalence charge transfer (IVCT) between Fe²⁺ and Fe³⁺ centers (Correct answer)
Metal-to-ligand charge transfer (MLCT) from iron to CN⁻ π*

Correct answer: Intervalence charge transfer (IVCT) between Fe²⁺ and Fe³⁺ centers

Prussian blue's deep blue color arises from intervalence charge transfer where an electron moves between Fe²⁺ (low-spin, C-bound) and Fe³⁺ (high-spin, N-bound) sites.

Question 17: In electrospray ionization (ESI) mass spectrometry, multiply charged ions are commonly observed. For a protein of molecular weight 10,000 Da carrying 10 protons, what is the observed m/z?

1,000
999
10,000
1,001 (Correct answer)

Correct answer: 1,001

With 10 protons added (each +1 Da), m/z = (10,000 + 10×1)/10 = 10,010/10 = 1,001.

Question 18: The Born-Oppenheimer approximation in molecular quantum mechanics assumes that:

Relativistic effects are negligible for light atoms
Nuclear and electronic motions can be separated due to mass differences (Correct answer)
Electron spin is negligible
All bonds are harmonic

Correct answer: Nuclear and electronic motions can be separated due to mass differences

Because nuclei are ~1836 times heavier than electrons, electrons adjust instantaneously to nuclear positions, allowing separation of their wavefunctions.

Question 19: Collision theory predicts the pre-exponential factor A in the Arrhenius equation. The steric factor p (0 < p ≤ 1) corrects for:

The fraction of collisions with sufficient energy
The reduced mass of the colliding pair
Quantum tunneling through the barrier
The fraction of collisions with the correct molecular orientation (Correct answer)

Correct answer: The fraction of collisions with the correct molecular orientation

The steric factor p accounts for the fact that not all geometrically successful collisions have the correct orientation for reaction.

Question 20: What is the primary purpose of a heat exchanger network in an industrial chemical plant?

To increase reaction conversion
To recover and reuse thermal energy between process streams (Correct answer)
To maintain catalyst activity
To control reactor pressure

Correct answer: To recover and reuse thermal energy between process streams

Heat exchanger networks use hot process streams to preheat cold ones, minimizing external utility consumption through energy integration.

Question 21: Which of the following is an example of a [3,3]-sigmatropic rearrangement?

Cope rearrangement (Correct answer)
Wagner–Meerwein rearrangement
Pinacol rearrangement
Beckmann rearrangement

Correct answer: Cope rearrangement

The Cope rearrangement is a thermal, concerted [3,3]-sigmatropic rearrangement of a 1,5-diene via a chair-like transition state.

Question 22: The Ellingham diagram is used in inorganic chemistry to predict:

The electrode potentials of metals in standard electrochemical cells
The kinetics of corrosion in aqueous environments at various pH values
The thermodynamic feasibility of reducing one metal oxide with another metal or carbon (Correct answer)
The crystal field stabilization energies of transition metal oxides

Correct answer: The thermodynamic feasibility of reducing one metal oxide with another metal or carbon

The Ellingham diagram plots ΔG° of oxide formation vs. temperature; a metal or carbon whose line lies below another oxide's line can thermodynamically reduce that oxide.

Question 23: Pa is the SI unit for pressure. equivalent to

1N/m² (Correct answer)
1Nm
1N/M
1N/m

Correct answer: 1N/m²

Pressure is fundamentally defined as force applied per unit area. In the International System of Units (SI), the unit for force is the Newton (N), and the unit for area is the square meter (m²). Therefore, one Pascal (Pa), the SI unit for pressure, is equivalent to one Newton per square meter (1 N/m²).

Question 24: Which regulatory designation expedites development of drugs for serious conditions with unmet medical need in the US?

Accelerated Approval
Orphan Drug Designation
Breakthrough Therapy Designation (Correct answer)
Fast Track Designation

Correct answer: Breakthrough Therapy Designation

Breakthrough Therapy Designation provides intensive FDA guidance and faster review for drugs showing substantial improvement over existing therapies on clinically significant endpoints.

Question 25: What chemical principle explains why mercury is particularly toxic in aquatic environments — specifically the methylation process?

Sulfate-reducing bacteria convert inorganic mercury to lipophilic methylmercury that bioaccumulates (Correct answer)
Mercury is absorbed only through direct contact with Hg0 vapor
Mercury reacts with dissolved oxygen to form HgO nanoparticles
Inorganic Hg2+ is more bioavailable than methylmercury

Correct answer: Sulfate-reducing bacteria convert inorganic mercury to lipophilic methylmercury that bioaccumulates

Anaerobic sulfate-reducing bacteria methylate inorganic Hg2+ to methylmercury (CH3Hg+), which is lipophilic, crosses biological membranes, and biomagnifies in food chains.

Question 26: The Arrhenius equation k = Ae^(−Ea/RT) predicts that a plot of ln k versus 1/T has a slope of:

−Ea
Ea/R
−Ea/R (Correct answer)
Ea/k_B

Correct answer: −Ea/R

Taking the natural log: ln k = ln A − Ea/(RT), so the slope of ln k vs. 1/T equals −Ea/R.

Question 27: One particle is released in the initial stage of the disintegration of uranium.

Gamma particle
Alpha particle (Correct answer)
Electron
Beta particle

Correct answer: Alpha particle

Uranium-238, the most abundant isotope of uranium, primarily undergoes alpha decay as its initial mode of radioactive disintegration. During alpha decay, an alpha particle (a helium nucleus, 4He) is emitted from the nucleus, transforming uranium-238 into thorium-234. This process is the first step in the long uranium decay series.

Question 28: Which industrial separation technique is used to purify para-xylene from a mixed C8 aromatics stream using zeolite adsorbents?

Cryogenic fractional distillation
Simulated moving bed (SMB) chromatographic separation (Correct answer)
Extractive distillation with sulfolane
Membrane pervaporation

Correct answer: Simulated moving bed (SMB) chromatographic separation

The UOP Parex process uses a simulated moving bed with zeolite adsorbent (e.g., faujasite) to selectively adsorb p-xylene from C8 isomers.

Question 29: What are persistent organic pollutants (POPs) characterized by?

High volatility and short atmospheric lifetime
Rapid photodegradation in surface waters
High water solubility and rapid biodegradation
Resistance to degradation, lipophilicity, long-range transport, and toxicity (Correct answer)

Correct answer: Resistance to degradation, lipophilicity, long-range transport, and toxicity

POPs are defined by their persistence, bioaccumulation in lipids, potential for long-range atmospheric transport, and adverse health and ecological effects.

Question 30: What theory of drug-receptor interactions maintains that a receptor is in a state of dynamic equilibrium between an activated form (Ro), which is responsible for the biological response, and an inactive form (To), even in the absence of drugs?

Activation-Aggregation Theory (Correct answer)
Induced fit theory
Occupation theory
Macromolecular Perturbation Theory

Correct answer: Activation-Aggregation Theory

The Activation-Aggregation Theory (also known as the Two-State Model or Conformational Selection Model) proposes that receptors exist in a dynamic equilibrium between an active (Ro or R*) and an inactive (To or R) conformational state, even in the absence of a ligand. Agonists preferentially bind to and stabilize the active state, shifting the equilibrium towards a biological response, while inverse agonists stabilize the inactive state.

Question 31: In the context of reactor design, what does the Damköhler number (Da) represent?

Ratio of convective to diffusive mass transfer
Ratio of heat generated to heat removed
Ratio of reactor volume to catalyst surface area
Ratio of reaction rate to mass transfer rate (or residence time) (Correct answer)

Correct answer: Ratio of reaction rate to mass transfer rate (or residence time)

The Damköhler number (Da = reaction rate / convective transport rate) indicates whether a system is reaction-limited (Da<<1) or transport-limited (Da>>1).

Question 32: Which strategy is used to overcome rapid metabolism of a drug by deuterium incorporation?

Deuterium increases logP to reduce hepatic extraction
Deuterium forms stronger hydrogen bonds with plasma proteins
Deuterium blocks CYP3A4 active site sterically
Deuterium isotope effect slows C–H bond cleavage at metabolic sites (Correct answer)

Correct answer: Deuterium isotope effect slows C–H bond cleavage at metabolic sites

Replacing metabolically vulnerable C–H bonds with C–D bonds exploits the primary kinetic isotope effect, slowing oxidative metabolism at those sites.

Question 33: In inductively coupled plasma mass spectrometry (ICP-MS), what is the primary purpose of the collision/reaction cell?

To nebulize the sample solution
To separate isotopes by mass
To remove polyatomic interferences (Correct answer)
To ionize the sample

Correct answer: To remove polyatomic interferences

The collision/reaction cell uses gases like helium or hydrogen to eliminate polyatomic spectral interferences that overlap with analyte masses.

Question 34: Of the following, which is NOT a representation of a chemical process?

Semantic diagram
Process-flow diagram
Block flow diagram
Flow chart (Correct answer)

Correct answer: Flow chart

In chemical engineering, specific and standardized diagrams are used to represent chemical processes, such as Block Flow Diagrams (BFD) and Process Flow Diagrams (PFD). While a 'flow chart' is a general diagram showing steps in a process, it is a broad term and not a specific, standardized type of chemical process representation in the same way BFDs or PFDs are.

Question 35: Why is there a need for separation if just 5% of ethylene is transformed to ethylene glycol?

To start an intermediate reaction
To recover the unreacted Ethylene Glycol (Correct answer)
To feed more reactant to the reacting mixture
To remove the ethylene glycol formed

Correct answer: To recover the unreacted Ethylene Glycol

If only 5% of ethylene is transformed into ethylene glycol, it means 95% of the initial ethylene remains unreacted. For the process to be economically viable and environmentally responsible, this large quantity of unreacted ethylene must be separated from the product (ethylene glycol) and subsequently recovered. The recovered unreacted ethylene can then be recycled back into the reactor, significantly improving the overall process efficiency and reducing raw material costs.

Question 36: Which Fischer-Tropsch derived fuel synthesis product distribution is described by the Anderson-Schulz-Flory (ASF) distribution?

Molecular weight distribution of polymers formed on Ziegler-Natta catalysts
Carbon number distribution of hydrocarbons produced as a function of chain growth probability α (Correct answer)
Isomer ratio of branched versus linear alkanes from reforming
Particle size distribution of catalyst after attrition in a fluidized bed

Correct answer: Carbon number distribution of hydrocarbons produced as a function of chain growth probability α

The ASF distribution predicts the mole fraction of each Cn hydrocarbon product from Fischer-Tropsch synthesis using the chain growth probability parameter α.

Question 37: In NMR spectroscopy of biomolecules, what is the NOE (Nuclear Overhauser Effect) used to determine?

The pKa values of ionizable residues in the active site
The molecular weight of a protein from its diffusion coefficient
The 3D structure of proteins by measuring through-space distances between protons < 5 Å apart (Correct answer)
The primary sequence of a protein from its fragmentation pattern

Correct answer: The 3D structure of proteins by measuring through-space distances between protons < 5 Å apart

The NOE provides distance restraints between protons within ~5 Å of each other, and these restraints are used with computational methods to determine solution-phase 3D protein structures.

Question 38: CYP3A4 is responsible for metabolizing approximately what percentage of marketed drugs?

25–30%
10–15%
50–60% (Correct answer)
75–80%

Correct answer: 50–60%

CYP3A4 is the most abundant hepatic cytochrome P450 and metabolizes approximately 50–60% of marketed pharmaceuticals.

Question 39: What is the glass transition temperature (Tg) of a polymer?

The temperature at which thermal degradation begins
The melting point of crystalline polymer domains
The temperature above which amorphous regions transition from a glassy to a rubbery state (Correct answer)
The temperature at which the polymer crystallizes from the melt

Correct answer: The temperature above which amorphous regions transition from a glassy to a rubbery state

The Tg marks the reversible transition of amorphous polymer segments from a rigid glassy state to a mobile, rubbery state as temperature increases.

Question 40: Choose the answer that has nothing to do with homogeneous mixture.

It has homogeneous composition
Its example is solution of sand in water (Correct answer)
It has single phase
It is composed of two or more different molecular or ionic substances

Correct answer: Its example is solution of sand in water

A homogeneous mixture has a uniform composition and properties throughout, appearing as a single phase (e.g., sugar dissolved in water). A solution of sand in water, however, is a heterogeneous mixture because the sand particles do not dissolve and remain visibly distinct, forming separate phases from the water.

Question 41: Which computational method is most appropriate for predicting the binding pose of a small molecule in a known protein crystal structure?

Homology modeling
Quantitative structure-activity relationship (QSAR)
Molecular docking (Correct answer)
Molecular dynamics (MD) simulation

Correct answer: Molecular docking

Molecular docking algorithms score and rank binding poses of small molecules within a defined protein binding site derived from crystallographic data.

Question 42: In atomic absorption spectroscopy (AAS), the hollow cathode lamp (HCL) is used because it emits:

Narrow-line radiation matching the analyte's absorption wavelength (Correct answer)
Broad-band continuum radiation for background correction
UV radiation to photoionize the analyte
Infrared radiation to excite vibrational modes

Correct answer: Narrow-line radiation matching the analyte's absorption wavelength

The HCL emits narrow atomic lines of the same element as its cathode, perfectly matching the absorption profile of the analyte atoms.

Question 43: In gas chromatography, the Kovats retention index is used to:

Express analyte retention relative to n-alkane standards (Correct answer)
Optimize carrier gas flow rate
Determine the absolute concentration of an analyte
Measure column efficiency in theoretical plates

Correct answer: Express analyte retention relative to n-alkane standards

The Kovats retention index expresses analyte retention as a linear interpolation between bracketing n-alkanes, making retention data transferable across columns and labs.

Question 44: What is the chemical basis of disulfide bond formation in protein folding?

A glutamine and asparagine residue condense to form an isopeptide bond
Two cysteine thiol groups (-SH) are oxidized to form a covalent S–S bridge (Correct answer)
Two histidine residues coordinate a zinc ion to form a structural crosslink
Serine and threonine hydroxyl groups condense to form ether linkages

Correct answer: Two cysteine thiol groups (-SH) are oxidized to form a covalent S–S bridge

Disulfide bonds form when two cysteine thiol groups lose electrons (oxidation) in the oxidizing environment of the ER lumen, catalyzed by protein disulfide isomerase (PDI).

Question 45: Which mechanism of resistance to β-lactam antibiotics is most clinically significant?

Mutation of the 30S ribosomal subunit
Overexpression of efflux pumps
Production of β-lactamase enzymes (Correct answer)
Decreased outer membrane permeability

Correct answer: Production of β-lactamase enzymes

β-Lactamase production is the predominant resistance mechanism; these enzymes hydrolyze the β-lactam ring, rendering the antibiotic inactive.

Question 46: In density functional theory (DFT), the exchange-correlation functional approximates which quantity?

Electrostatic Coulomb energy
Many-body exchange and correlation effects (Correct answer)
Kinetic energy of electrons
Nuclear repulsion energy

Correct answer: Many-body exchange and correlation effects

The exchange-correlation functional in DFT approximates the complex many-body exchange and correlation effects that cannot be computed exactly.

Question 47: The canonical partition function Q for a system of N distinguishable, independent particles is related to the single-particle partition function q by:

Q = q^N (Correct answer)
Q = q^N / N!
Q = N! · q
Q = Nq

Correct answer: Q = q^N

For distinguishable independent particles, the system partition function is simply the product of individual partition functions: Q = q^N.

Question 48: What is the role of hydroxyl radicals (•OH) in tropospheric chemistry?

They catalyze stratospheric ozone depletion
They are the main cause of acid rain
They act as the atmosphere's primary oxidant, initiating degradation of VOCs and methane (Correct answer)
They absorb UV radiation in the stratosphere

Correct answer: They act as the atmosphere's primary oxidant, initiating degradation of VOCs and methane

Hydroxyl radicals are the dominant oxidant in the troposphere, reacting with VOCs, CH4, and CO to initiate their atmospheric degradation.

Question 49: Solvent and solute concentrations can both be stated as

moles
volume
mass
all of these (Correct answer)

Correct answer: all of these

Concentrations of both solvents and solutes can be expressed using various units depending on the context. These include mass-based units (e.g., grams, kilograms, mass percentage), volume-based units (e.g., milliliters, liters, volume percentage), and mole-based units (e.g., moles, molarity). Therefore, all these options represent valid ways to state concentrations.

Question 50: The zero-point energy of a quantum harmonic oscillator with frequency ν is:

³∕₂hν
0
hν
½hν (Correct answer)

Correct answer: ½hν

The ground state (n=0) energy of a harmonic oscillator is ½hν, called the zero-point energy.

Question 51: What distinguishes a kinetic enolate from a thermodynamic enolate?

Kinetic enolates are always formed from symmetrical ketones
Kinetic enolates are formed at high temperature using weak bases
Thermodynamic enolates form faster because the less substituted alkene is less hindered
Kinetic enolates are the less substituted and form faster under low-temperature, strong-base conditions (Correct answer)

Correct answer: Kinetic enolates are the less substituted and form faster under low-temperature, strong-base conditions

Under low temperature and strong, hindered base (e.g., LDA), deprotonation of the more accessible (less substituted) position is faster, giving the kinetic enolate.

Question 52: When an unsaturated solution is overconcentrated, it transforms into

colloidal solution
saturated solution (Correct answer)
unsaturated solution
supersaturated solution

Correct answer: saturated solution

An unsaturated solution contains less solute than the maximum amount that can be dissolved at a given temperature. When more solute is added to an unsaturated solution until the maximum solubility limit is reached, the solution becomes saturated. At this point, no more solute can dissolve, and any additional solute will typically remain undissolved or precipitate out.

Question 53: What does the term 'basis set superposition error' (BSSE) describe in computational chemistry?

Error from truncating the Hamiltonian operator
Error from using an incomplete exchange-correlation functional
Artificial lowering of energy when fragments share basis functions (Correct answer)
Inaccuracy in computing nuclear repulsion

Correct answer: Artificial lowering of energy when fragments share basis functions

BSSE arises when interacting fragments use each other's basis functions, artificially lowering the computed interaction energy.

Question 54: For a second-order reaction A → products with rate law v = k[A]², the half-life t₁/₂ depends on initial concentration [A]₀ as:

t₁/₂ = [A]₀ / (2k)
t₁/₂ = 1 / (k[A]₀) (Correct answer)
t₁/₂ = ln2 / k
t₁/₂ = 2 / (k[A]₀)

Correct answer: t₁/₂ = 1 / (k[A]₀)

Integration of the second-order rate law gives t₁/₂ = 1/(k[A]₀), showing the half-life is inversely proportional to initial concentration.

Question 55: Surface-adsorbed chemicals are known as surfactants, and surface tension is

varied
remain constant
increased
decreased (Correct answer)

Correct answer: decreased

Surfactants are compounds that, when added to a liquid, reduce its surface tension. They achieve this by adsorbing at the liquid-air or liquid-liquid interface, disrupting the cohesive forces between liquid molecules at the surface. This property makes them useful in applications like detergents, emulsifiers, and wetting agents.

Question 56: Which algorithm is most commonly used to locate transition states on a potential energy surface?

Simulated annealing
Monte Carlo random walk
Nudged elastic band (NEB) or quasi-Newton eigenvector following (Correct answer)
Steepest descent minimization

Correct answer: Nudged elastic band (NEB) or quasi-Newton eigenvector following

Methods like nudged elastic band and quasi-Newton eigenvector following locate saddle points (transition states) on the PES.

Question 57: The Sackur-Tetrode equation gives the absolute entropy of a monatomic ideal gas. Doubling the volume at constant temperature and N changes the entropy by:

−Nk_B ln 2
2Nk_B ln 2
Nk_B ln 2 (Correct answer)
Nk_B / 2

Correct answer: Nk_B ln 2

From S = Nk_B[ln(V/N) + ...], doubling V increases S by Nk_B ln(2), consistent with a reversible isothermal expansion.

Question 58: The transmitted radiations are of the following types when the EMR radiations travel through the medium:

None of these
High Energy
Low intensity
High intensity (Correct answer)

Correct answer: High intensity

When electromagnetic radiation (EMR) travels through a medium, some of its energy can be absorbed or scattered, while the remaining portion is transmitted. If the medium is largely transparent to the EMR, or if we are referring to the component of EMR that successfully passes through without significant absorption, then the transmitted radiation will retain a high intensity. In spectrophotometry, we measure the reduction in intensity due to absorption, meaning the transmitted light is of lower intensity than the incident light if absorption occurs, but the question implies the nature of the transmitted radiation itself.

Question 59: Which of the following processes employs lead tetraacetate to dissolve a glycol's carbon-carbon bond?

Criegee oxidation (Correct answer)
Swern oxidation
Jones oxidation
Baeyer-Villiger Oxidation

Correct answer: Criegee oxidation

The Criegee oxidation is a specific organic reaction that employs lead tetraacetate (Pb(OAc)4) to selectively cleave the carbon-carbon bond of vicinal diols (glycols). This oxidative cleavage typically results in the formation of aldehydes or ketones. It is a valuable method in organic synthesis for breaking C-C bonds in a controlled manner.

Question 60: A metal and a chemical are combined to generate a coordination complex.

None of them
Another Metal
Salt
Ligand (Correct answer)

Correct answer: Ligand

In coordination chemistry, a ligand is a molecule or ion that binds to a central metal atom or ion to form a coordination complex. Ligands act as Lewis bases, donating one or more electron pairs to the metal center to form coordinate covalent bonds. This interaction is fundamental to the structure and reactivity of coordination compounds.

Question 61: What changes the physiological circumstances in a biochemical plant?

The micro-organism (Correct answer)
The reaction
The ambient conditions
State of the products

Correct answer: The micro-organism

In a biochemical plant, the microorganism itself is the primary driver of the biochemical reactions and significantly alters the physiological environment. Its metabolic processes consume nutrients, produce metabolites, and influence factors like pH, temperature, and oxygen levels within the bioreactor. Therefore, the specific microorganism and its activity are central to defining the physiological circumstances.

Question 62: There are several primary vibrations for linear molecules, including

3N-6
3N-5 (Correct answer)
2N-6
2N-5

Correct answer: 3N-5

The number of fundamental vibrational modes (normal modes) for a molecule depends on its geometry and the number of atoms (N). For linear molecules, there are 3N - 5 vibrational modes, as two rotational degrees of freedom are removed. For non-linear molecules, the formula is 3N - 6.

Question 63: Which word applies to a mole of carbon and a mole of helium?

Mass
molecules
atom (Correct answer)
density

Correct answer: atom

A mole of any element contains Avogadro's number (approximately 6.022 x 10^23) of its constituent particles. For elemental substances like carbon and helium, these constituent particles are individual atoms. Therefore, a mole of carbon contains Avogadro's number of carbon atoms, and a mole of helium contains Avogadro's number of helium atoms.

Question 64: In molecular mechanics force fields (e.g., AMBER, CHARMM), what type of interactions are typically NOT included?

Angle bending
Quantum mechanical electron correlation (Correct answer)
Torsional potentials
Bond stretching

Correct answer: Quantum mechanical electron correlation

Molecular mechanics force fields use classical potential energy terms and cannot model quantum mechanical effects such as electron correlation or bond breaking.

Question 65: In Density Functional Theory (DFT), the Hohenberg-Kohn theorem proves that the ground-state energy of a many-electron system is a unique functional of:

The electron density ρ(r) (Correct answer)
The external potential V_ext alone
The kinetic energy operator
The many-body wavefunction Ψ

Correct answer: The electron density ρ(r)

The first Hohenberg-Kohn theorem establishes a one-to-one mapping between the ground-state electron density ρ(r) and the external potential, making all ground-state properties functionals of ρ(r).

Question 66: What is the significance of the octanol-water partition coefficient (Kow) for environmental fate of organic pollutants?

It predicts the rate of photodegradation in surface waters
It measures the rate of volatilization from soil
It predicts bioaccumulation potential and hydrophobicity (Correct answer)
It determines the pH buffering capacity of the compound

Correct answer: It predicts bioaccumulation potential and hydrophobicity

A high logKow indicates a compound is lipophilic, predicting strong bioaccumulation in fatty tissues and partitioning into organic matter.

Question 67: Pick substances that can be converted into chelating agents.

Bidentate
Tridentate
Tetradentate
All of them (Correct answer)

Correct answer: All of them

Chelating agents are ligands that can form multiple coordinate bonds with a single metal ion, creating a stable, ring-like structure known as a chelate. Ligands are categorized by their denticity, which refers to the number of donor atoms they use to bind to the metal center. Bidentate (two donor atoms), tridentate (three donor atoms), and tetradentate (four donor atoms) ligands are all capable of acting as effective chelating agents.

Question 68: The Nernst equation for an electrochemical cell at 298 K modifies the standard cell potential as E = E° − (0.0257/n)·ln Q. For a cell with n=2 and reaction quotient Q=100, the correction to E° is approximately:

+0.118 V
−0.059 V (Correct answer)
−0.118 V
+0.059 V

Correct answer: −0.059 V

ΔE = −(0.0257/2)·ln(100) = −(0.01285)·4.605 ≈ −0.059 V.

Question 69: Which property of carbon nanotubes makes them attractive for reinforcing composite materials?

Their exceptionally high tensile strength (up to ~100 GPa) combined with low density (Correct answer)
Their hydrophilicity enabling bonding with polymer matrices
Their high density and optical transparency
Their high thermal conductivity alone

Correct answer: Their exceptionally high tensile strength (up to ~100 GPa) combined with low density

Carbon nanotubes have tensile strengths ~100 times that of steel at one-sixth the weight, making them ideal candidates for lightweight high-strength composite reinforcement.

Question 70: Which technique is most diagnostic for distinguishing terminal, bridging, and face-capping carbonyl ligands in metal carbonyl clusters?

Mass spectrometry
¹H NMR spectroscopy
IR spectroscopy (ν(CO) stretching frequencies) (Correct answer)
UV-Vis spectroscopy

Correct answer: IR spectroscopy (ν(CO) stretching frequencies)

IR spectroscopy directly measures ν(CO) frequencies: terminal CO (~2000 cm⁻¹), bridging CO (~1800 cm⁻¹), and face-capping CO appear at progressively lower wavenumbers.

Question 71: What is the significance of the therapeutic index (TI) in pharmaceutical development?

It ranks the potency of drugs within the same pharmacological class
It predicts the duration of drug action in plasma
It measures the rate of drug absorption
It quantifies the ratio between toxic dose and effective dose, indicating the safety margin (Correct answer)

Correct answer: It quantifies the ratio between toxic dose and effective dose, indicating the safety margin

The therapeutic index (TD50/ED50) describes the safety margin of a drug; a narrow TI (e.g., warfarin, digoxin, lithium) requires careful therapeutic drug monitoring.

Question 72: The Boltzmann entropy formula S = k_B ln(Ω) implies that the entropy of a perfect crystal at 0 K is zero because:

There is only one accessible microstate (Ω=1) (Correct answer)
All atomic vibrations cease
The partition function equals N
The heat capacity becomes zero

Correct answer: There is only one accessible microstate (Ω=1)

A perfect crystal at 0 K has a unique ground state arrangement, so Ω = 1 and S = k_B ln(1) = 0, consistent with the Third Law.

Question 73: In cross-linked polymer networks such as vulcanized rubber, what is the primary chemical change introduced during vulcanization?

Introduction of ester linkages between chain ends
Addition of plasticizers to lower the glass transition temperature
Formation of polysulfide cross-links between polyisoprene chains via sulfur (Correct answer)
Grafting of styrene onto the rubber backbone

Correct answer: Formation of polysulfide cross-links between polyisoprene chains via sulfur

Vulcanization introduces polysulfide (C-S-S-C) cross-links between polyisoprene chains via reaction with elemental sulfur, converting the linear rubber into an elastic three-dimensional network.

Question 74: Choose the inaccurate composition percentage expression.

m/d% (Correct answer)
m/m%
m/v %
v/v %

Correct answer: m/d%

Common composition percentage expressions include mass/mass (m/m%), mass/volume (m/v%), and volume/volume (v/v%). These units clearly define the components being measured. The expression 'm/d%' is not a standard or recognized unit for expressing composition percentage in chemistry, making it the inaccurate option.

Question 75: What is the Ramachandran plot used for in protein structural analysis?

Displaying the allowed phi (φ) and psi (ψ) backbone dihedral angles of amino acid residues in a protein (Correct answer)
Showing the distribution of amino acid compositions in a protein
Illustrating the secondary structure assignment along the protein sequence
Mapping the hydrophobic core residues of a folded protein

Correct answer: Displaying the allowed phi (φ) and psi (ψ) backbone dihedral angles of amino acid residues in a protein

The Ramachandran plot visualizes sterically allowed backbone conformations; residues in disallowed regions indicate model errors in X-ray or cryo-EM structures.

Question 76: The Hansch analysis in medicinal chemistry uses the partition coefficient (π) to quantify which parameter?

Substituent lipophilicity (Correct answer)
Molar refractivity
pKa contribution
Molecular flexibility

Correct answer: Substituent lipophilicity

The Hansch π parameter measures the relative lipophilicity contribution of a substituent compared to hydrogen (π = logP_substituted − logP_unsubstituted).

Question 77: In VSEPR theory, which molecular geometry results from an AX₄E₂ electron domain arrangement?

Trigonal bipyramidal
Octahedral
Square pyramidal
Square planar (Correct answer)

Correct answer: Square planar

AX₄E₂ has 6 electron domains (4 bonding + 2 lone pairs) arranged octahedrally; the two lone pairs occupy axial positions, giving a square planar molecular geometry.

Question 78: In DNA replication, what is the chemical basis for the 3'→5' proofreading activity of DNA polymerase?

DNA polymerase has an intrinsic 3'→5' exonuclease domain that excises incorrectly incorporated nucleotides (Correct answer)
A separate exonuclease enzyme removes mismatched bases after replication
Mismatch repair proteins act during replication to immediately fix errors
The DNA helicase corrects mismatches as it unwinds the double helix

Correct answer: DNA polymerase has an intrinsic 3'→5' exonuclease domain that excises incorrectly incorporated nucleotides

DNA polymerase III possesses a 3'→5' exonuclease domain that recognizes and excises mismatched 3'-terminal nucleotides, then re-synthesizes the correct sequence.

Question 79: In a Claisen condensation, what acts as the leaving group from the tetrahedral intermediate?

An alkoxide ion (Correct answer)
A hydride ion
A hydroxide ion
A carbanion

Correct answer: An alkoxide ion

The alkoxide ion (–OR) leaves from the tetrahedral intermediate, regenerating the carbonyl and forming the β-ketoester product.

Question 80: What amount of solute is needed to prepare 300 ml of 0.8M CaCl2 (mol.wt:111 g/mol)?

26.64 g (Correct answer)
2.664 g
0.2664 g
2664 g

Correct answer: 26.64 g

First, calculate the moles of CaCl₂ needed: Moles = Molarity × Volume (in Liters) = 0.8 mol/L × 0.300 L = 0.24 moles. Next, convert moles to mass using the molar mass: Mass = Moles × Molar Mass = 0.24 mol × 111 g/mol = 26.64 g. Therefore, 26.64 g of CaCl₂ is required.

Question 81: The rate at which phenolphthalein fades in basic solution is

0th order
3rd order
1st order (Correct answer)
2nd order

Correct answer: 1st order

The fading of phenolphthalein in a basic solution is a classic example of a chemical reaction whose rate depends on the concentration of the reactants. Experimental studies typically show that this reaction follows first-order kinetics with respect to phenolphthalein, meaning its rate of disappearance is directly proportional to its concentration.

Question 82: What is the primary chemical reaction responsible for the formation of tropospheric ozone in urban smog?

Oxidation of methane by OH radicals alone
Direct emission of O3 from vehicles
Photolysis of NO2 followed by O + O2 → O3 (Correct answer)
Reaction of SO2 with sunlight

Correct answer: Photolysis of NO2 followed by O + O2 → O3

Tropospheric ozone forms when UV light photolyzes NO2 to produce atomic oxygen, which then combines with O2 to form O3.

Question 83: Which endogenous enzyme system is the primary target of proton pump inhibitors (PPIs) like omeprazole?

Carbonic anhydrase in renal tubules
H⁺/K⁺-ATPase in gastric parietal cells (Correct answer)
Na⁺/K⁺-ATPase in cardiac muscle
Ca²⁺-ATPase in smooth muscle

Correct answer: H⁺/K⁺-ATPase in gastric parietal cells

PPIs irreversibly inhibit the H⁺/K⁺-ATPase (proton pump) in gastric parietal cells, blocking the final step of gastric acid secretion.

Question 84: What is the principle behind FRET (Förster Resonance Energy Transfer) in biochemical assays?

Two fluorophores absorb the same photon simultaneously
Non-radiative energy transfers from a donor fluorophore to an acceptor when they are within ~10 nm of each other (Correct answer)
Electrons transfer directly between two fluorophores via tunneling
A fluorophore transfers energy to oxygen, generating reactive singlet oxygen

Correct answer: Non-radiative energy transfers from a donor fluorophore to an acceptor when they are within ~10 nm of each other

FRET occurs via dipole-dipole coupling between a donor and acceptor fluorophore; its efficiency falls off as the inverse 6th power of distance, making it a molecular ruler for ~1–10 nm distances.

Question 85: In polymer production, what distinguishes a Ziegler-Natta catalyst from a metallocene catalyst?

Ziegler-Natta catalysts require higher temperatures
Ziegler-Natta catalysts only polymerize ethylene
Metallocene catalysts produce narrower molecular weight distributions due to single-site active centers (Correct answer)
Metallocene catalysts are heterogeneous while Ziegler-Natta are homogeneous

Correct answer: Metallocene catalysts produce narrower molecular weight distributions due to single-site active centers

Metallocenes are single-site catalysts giving narrow PDI (~2), whereas Ziegler-Natta catalysts have multiple active sites producing broader distributions.

Question 86: In the context of soil contamination, what does the Koc value measure?

The toxicity of a compound to soil organisms
The rate of microbial degradation of a compound
The organic carbon-normalized partition coefficient between soil and water (Correct answer)
The volatility of a pollutant from soil

Correct answer: The organic carbon-normalized partition coefficient between soil and water

Koc is the organic carbon-normalized partition coefficient, indicating how strongly a hydrophobic organic pollutant adsorbs to soil organic matter relative to pore water.

Question 87: For a chain reaction mechanism, the steady-state approximation applied to radical intermediates gives the rate law. Which step determines the overall reaction order for a long chain?

The propagation step (Correct answer)
The branching step
The initiation step
The termination step

Correct answer: The propagation step

In a long chain where the chain length >> 1, propagation steps dominate and determine the observed rate law and reaction order.

Question 88: The residual entropy of ice at 0 K arises from:

Nuclear spin degeneracy of oxygen-17
Lattice defects in the crystal structure
Isotopic disorder of hydrogen and oxygen
Random orientation of hydrogen bonds following the ice rules (Correct answer)

Correct answer: Random orientation of hydrogen bonds following the ice rules

Pauling showed that hydrogen-bond proton positions in ice are not unique at 0 K, giving S_residual = Nk_B ln(3/2) per mole.

Question 89: What is the key biochemical role of glutathione (GSH) in cellular protection?

It transports electrons in the mitochondrial electron transport chain
It scavenges reactive oxygen species and detoxifies electrophilic xenobiotics via GSH-S-transferases (Correct answer)
It is a coenzyme for fatty acid elongation
It regulates blood glucose by activating insulin receptor kinase

Correct answer: It scavenges reactive oxygen species and detoxifies electrophilic xenobiotics via GSH-S-transferases

Glutathione (γ-Glu-Cys-Gly) acts as the cell's major antioxidant, reducing H2O2 via glutathione peroxidase and conjugating electrophiles via glutathione S-transferases for detoxification.

Question 90: In chemical biology, what is a 'warhead' in the context of covalent inhibitor drug design?

A reactive electrophilic group that forms a covalent bond with a nucleophilic residue in the target protein (Correct answer)
The fluorescent reporter group on a probe molecule
The pharmacophore that determines binding specificity
A prodrug moiety that is cleaved in vivo to release the active drug

Correct answer: A reactive electrophilic group that forms a covalent bond with a nucleophilic residue in the target protein

Warheads (e.g., acrylamides, chloroacetamides) are reactive electrophiles that covalently modify active-site nucleophiles (e.g., Cys, Lys), providing irreversible or slow-reversible inhibition.

Question 91: The diffusion coefficient D of a spherical particle in solution is given by the Stokes-Einstein equation D = k_BT/(6πηr). If the solvent viscosity η doubles at lower temperature while T decreases by 10%, D:

Increases slightly
Remains essentially unchanged
Increases proportionally to T
Decreases significantly (Correct answer)

Correct answer: Decreases significantly

D ∝ T/η; if η doubles and T falls ~10%, D decreases by roughly half (D ≈ 0.9T / 2η ≈ 0.45× original), a significant decrease.

Question 92: In industrial electrochemical production of chlorine and sodium hydroxide, what is the name of the modern membrane cell process that replaced the mercury cell?

Bayer process
Hall-Héroult process
Downs cell process
Chlor-alkali membrane cell process (e.g., Nafion membrane) (Correct answer)

Correct answer: Chlor-alkali membrane cell process (e.g., Nafion membrane)

Modern chlor-alkali plants use ion-exchange membranes (e.g., DuPont Nafion) to separate the anode (Cl2) and cathode (NaOH) compartments without mercury.

Question 93: Which method uses the Born-Oppenheimer approximation to separate nuclear and electronic motion?

Monte Carlo simulation
Ab initio quantum chemistry (Correct answer)
Molecular dynamics
Molecular mechanics

Correct answer: Ab initio quantum chemistry

Ab initio quantum chemistry relies on the Born-Oppenheimer approximation to treat nuclear and electronic degrees of freedom separately.

Question 94: Which of the following is not a relationship?

100L=100dm³
1m3=10cm³
1L=1dm³
1ml=1cm³ (Correct answer)

Correct answer: 1ml=1cm³

The relationship 1m³ = 10cm³ is incorrect. Since 1 meter (m) equals 100 centimeters (cm), 1 cubic meter (1 m³) is equivalent to (100 cm)³, which is 1,000,000 cm³. The other options represent correct standard unit conversions in chemistry: 1L = 1dm³, 1mL = 1cm³, and thus 100L = 100dm³.

Question 95: What is the function of a 'scrubber' in an industrial gas treatment system?

To remove gaseous pollutants or particulates by contacting gas with a liquid or solid sorbent (Correct answer)
To compress gas to high pressure
To crack heavy hydrocarbons into lighter fractions
To measure gas composition by spectrometry

Correct answer: To remove gaseous pollutants or particulates by contacting gas with a liquid or solid sorbent

Scrubbers absorb or react acidic gases (e.g., SO2, HCl, H2S) or particulates from process or flue gas streams using aqueous or alkaline solutions.

Question 96: What structural feature of phospholipid bilayers explains their selective permeability?

Membrane proteins form a continuous impermeable seal
The hydrophobic hydrocarbon core creates an energetic barrier that strongly excludes charged and polar molecules (Correct answer)
The charged phosphate headgroups create pores that allow ion transport
The fluid mosaic model requires lateral movement to transport molecules

Correct answer: The hydrophobic hydrocarbon core creates an energetic barrier that strongly excludes charged and polar molecules

The hydrophobic bilayer interior (ΔG ~ +20 kcal/mol for ion transfer) is highly impermeable to ions and polar molecules, while nonpolar gases (O2, CO2) diffuse freely.

Question 97: In industrial polymerization, what is 'living polymerization' and why is it industrially valuable?

A chain-growth process with no termination, enabling precise control of molecular weight and block copolymer synthesis (Correct answer)
Polymerization conducted in aqueous emulsion to produce latex particles
A step-growth process producing polymers with exactly two end groups
Polymerization using biological enzymes as catalysts for biodegradable plastics

Correct answer: A chain-growth process with no termination, enabling precise control of molecular weight and block copolymer synthesis

Living polymerization (e.g., ATRP, RAFT) lacks irreversible termination, producing narrow PDI polymers and enabling sequential block copolymer formation.

Question 98: What is the main mechanism of stratospheric ozone depletion by chlorofluorocarbons (CFCs)?

CFCs react directly with O2 to form ClO3
Cl• radicals from photolysis of CFCs catalytically destroy O3 (Correct answer)
CFCs absorb UV radiation and block it from reaching the stratosphere
CFCs raise stratospheric temperatures, slowing ozone production

Correct answer: Cl• radicals from photolysis of CFCs catalytically destroy O3

UV photolysis of CFCs releases Cl• radicals in the stratosphere, which catalytically destroy ozone via Cl• + O3 → ClO + O2 cycles.

Question 99: Which type of enzyme inhibition increases the apparent Km without affecting Vmax?

Uncompetitive inhibition
Non-competitive inhibition
Competitive inhibition (Correct answer)
Mixed inhibition

Correct answer: Competitive inhibition

Competitive inhibitors bind the active site and increase apparent Km (reduced substrate affinity) but can be overcome by excess substrate, leaving Vmax unchanged.

Question 100: Which of the following complexes contains an organic ligand with a single metal bond?

W(CH3)6 (Correct answer)
(η5-C6H6)2Ru
K[PtCl3(C2H4)]
(η5-C5H5)2Fe

Correct answer: W(CH3)6

W(CH3)6 contains six methyl (CH3) ligands, each forming a single sigma bond (W-C) directly with the tungsten metal center. This is a classic example of a metal-alkyl complex with single metal-carbon bonds. The other options involve pi-bonding (e.g., ethylene, cyclopentadienyl, benzene), where multiple carbon atoms of the ligand interact simultaneously with the metal, not through a single sigma bond.

Question 101: The substance is referred to as benzoin oxime.

None of them
Cupric acid
Cupron
Dioxime (Correct answer)

Correct answer: Dioxime

Benzoin oxime is an organic compound derived from benzoin and hydroxylamine. It is classified as a dioxime because it contains two oxime functional groups. This compound is known for its chelating properties and is often employed in analytical chemistry, particularly for the gravimetric determination of metal ions like copper.

MChem Master of Chemistry

The MChem (Master of Chemistry) is a 4-year integrated undergraduate/postgraduate degree accredited by the Royal Society of Chemistry (RSC), assessing students across core and advanced chemistry disciplines including organic, inorganic, physical, industrial, biochemical, and computational chemistry.

100

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120 min

Time Limit

70%

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