Free NEET MCQ Test Questions and Answers — Questions and Answers

Question 1: What is true about the following statements?

Larva of all cyclostomes return to freshwater after metamorphosis
All mammals have placenta
All Chondrichthyes are marine animals with a streamlined body with some exceptions (Correct answer)
Chelone and Testudo are able to maintain a constant body temperature

Correct answer: All Chondrichthyes are marine animals with a streamlined body with some exceptions

Chondrichthyes, or cartilaginous fishes (e.g., sharks, rays), are predominantly marine animals characterized by a streamlined body and a cartilaginous skeleton. While most species are found in marine environments, there are indeed some exceptions, such as certain rays and sharks that can inhabit brackish or freshwater. This statement accurately captures their general characteristics with the important nuance of exceptions.

Question 2: A table tennis ball with a conducting tip on it hangs between two metal plates and is supported by a thin thread. One plate is connected to the earth, while the other is to a high-voltage generator, with the ball in between.

Swings backward & forward hitting each plate in turn (Correct answer)
Hangs without moving
Is repelled by an earthed plate and stays there
Is attracted to the high voltage plate and stays there

Correct answer: Swings backward & forward hitting each plate in turn

When the conducting ball touches the high-voltage plate, it acquires the same charge and is then repelled by that plate while being attracted to the earthed plate. Upon contact with the earthed plate, the ball discharges or acquires an opposite charge, causing it to be repelled by the earthed plate and attracted back to the high-voltage plate. This continuous cycle of attraction and repulsion results in the ball swinging back and forth between the two plates.

Question 3: The corners of a cubic unit cell in a solid "AB" with a NaCl structure are occupied by "A" atoms. The solid's resulting stoichiometry is as follows if all the atoms with faces to one of the axes are eliminated:

A3B4 (Correct answer)
A4B3
A2B
AB2

Correct answer: A3B4

In a solid with a NaCl structure, one type of atom (A) forms an FCC lattice (corners and face centers), and the other (B) occupies octahedral voids (edge centers and body center), resulting in A4B4 initially. If atoms on faces perpendicular to one axis are eliminated, this typically refers to the two face-centered atoms on those opposite faces. These are A atoms, and each contributes 1/2 to the unit cell, so 1 A atom is effectively removed. B atoms, being at edge centers and the body center, are not affected. Thus, the stoichiometry becomes A3B4.

Question 4: Which of the following metal pollutants found in vehicle exhaust is the most hazardous?

Mercury
Lead (Correct answer)
Copper
Cadmium

Correct answer: Lead

Lead is widely recognized as the most hazardous metal pollutant found in vehicle exhaust. It is a neurotoxin that can cause severe developmental and neurological problems, especially in children, even at low exposure levels. Historically, leaded gasoline was a major source of environmental lead contamination, leading to widespread health concerns before its phase-out.

Question 5: Which of the following about the myelin sheath is incorrect?

Myelin sheath is seen only as an outermost layer of a whole Schwann cell. (Correct answer)
It is mainly secreted by the Schwann cells in the cranial and spinal nerves.
The gaps between two adjacent myelin sheaths are called nodes of Ranvier.
Schwann cells are lipid-rich cells enveloping the axon.

Correct answer: Myelin sheath is seen only as an outermost layer of a whole Schwann cell.

The statement that the myelin sheath is seen only as an outermost layer of a whole Schwann cell is incorrect. While Schwann cells do form the myelin sheath in the peripheral nervous system, the myelin itself is a multi-layered lipid-rich membrane that wraps around the axon, not just a single outermost layer. It is secreted by Schwann cells (PNS) and oligodendrocytes (CNS) and acts as an insulating layer, with gaps called Nodes of Ranvier.

Question 6: Which of the following multicellular animals lacks neurons or nerve cells that can react to stimuli?

Anemone
Hydra
Sponge (Correct answer)
Only a and b

Correct answer: Sponge

Sponges (Phylum Porifera) are the simplest multicellular animals and are unique in lacking true tissues, organs, and a nervous system. Unlike animals like anemones and hydra, which possess a rudimentary nerve net, sponges do not have neurons or nerve cells to react to stimuli in a coordinated manner. Their cellular responses are localized and independent.

Question 7: Which of the subsequent antibody subtypes is produced by a peanut hypersensitive person?

IgE (Correct answer)
IgA
IgM
IgD

Correct answer: IgE

Individuals with hypersensitivity reactions, such as a peanut allergy, produce a specific type of antibody called Immunoglobulin E (IgE). Upon exposure to the allergen, IgE antibodies bind to mast cells and basophils, triggering the release of histamine and other inflammatory mediators. This cascade of events leads to the characteristic symptoms of an allergic reaction, ranging from mild to severe anaphylaxis.

Question 8: In the presence of an attacking reagent, the displacement of electrons in numerous bonds is known as:

Hyper conjugation
Resonance
Electromeric effect (Correct answer)
Inductive effect

Correct answer: Electromeric effect

The electromeric effect is a temporary electronic effect observed in organic molecules containing multiple bonds (double or triple bonds) in the presence of an attacking reagent. It involves the complete transfer of a shared pair of pi (π) electrons to one of the bonded atoms. This displacement occurs to facilitate the attack of the reagent and is reversible once the reagent is removed.

Question 9: Rhododendron leaves curling is one instance of?

Thigmotropism
Thermotropism (Correct answer)
Phototropism
Hydrotropism

Correct answer: Thermotropism

Rhododendron leaves curling is an example of thermotropism, which is a plant's growth or movement response to changes in temperature. In cold temperatures, rhododendron leaves curl inwards and droop to reduce their surface area exposed to the cold, thereby minimizing water loss and protecting their delicate tissues from freezing damage. This is a survival mechanism to conserve water and energy.

Question 10: An increase in CO2 levels will result in:

Faster and deeper breathing (Correct answer)
Slower and deeper breathing
Slower and shallow breathing
No effect on breathing

Correct answer: Faster and deeper breathing

An increase in CO2 levels in the blood leads to a decrease in blood pH, making it more acidic. Chemoreceptors in the brainstem and major arteries detect this change and signal the respiratory center. In response, the body increases the rate and depth of breathing to expel more CO2, thereby restoring blood pH to its normal range.

Question 11: The nitrogenous waste that is least hazardous is generated by:

Insects and bony fishes
Frog and cartilaginous fishes
Birds and lizards (Correct answer)
Mammals and molluscs

Correct answer: Birds and lizards

Birds and lizards, along with most reptiles, excrete nitrogenous waste primarily as uric acid. Uric acid is the least hazardous form of nitrogenous waste because it is largely insoluble in water and can be excreted as a semi-solid paste, requiring very little water for its removal. This adaptation is crucial for conserving water in arid environments, making it less toxic than ammonia or urea.

Question 12: Cryolite is added to the charge in the electrolytic process of producing aluminium from refined bauxite in order to:

Dissolve bauxite and render it a conductor of electricity (Correct answer)
Protect aluminium produced from oxygen
Minimise the heat loss due to radiation
Lower the melting point of bauxite

Correct answer: Dissolve bauxite and render it a conductor of electricity

Cryolite (Na3AlF6) is added to the molten alumina (from bauxite) in the Hall-Héroult electrolytic process for aluminium production. Its primary role is to dissolve the alumina, forming an electrolyte that conducts electricity. While it also lowers the melting point of alumina, its main function is to create an electrically conductive solution, as molten alumina itself is a poor conductor.

Question 13: Which of the subsequent reagents can turn butanoic acid into butane?

CH3MgBr
NaOH / CaO
Red P / HI (Correct answer)
All of these

Correct answer: Red P / HI

Butanoic acid can be converted to butane through a reduction reaction using Red Phosphorus (Red P) and Hydroiodic Acid (HI). This powerful reducing agent system is capable of reducing carboxylic acids, as well as other functional groups like alcohols and aldehydes, completely to alkanes. The reaction involves the removal of oxygen atoms and the addition of hydrogen atoms.

Question 14: What will the particles' X-coordinates be in a system of bodies where the center of mass is at the origin?

Positive for some particles and negative for other particles (Correct answer)
Always negative for all the particles
Always positive for all particles
None of these

Correct answer: Positive for some particles and negative for other particles

If the center of mass of a system of bodies is at the origin, it means the weighted average position of all particles is zero. For this to be true, if some particles have positive X-coordinates, there must be other particles with negative X-coordinates to balance them out. It's impossible for all particles to have only positive or only negative X-coordinates, as that would shift the center of mass away from the origin.

Question 15: Which of the following is not an accurate differential?

G(dG = Gibbs free energy change)
S(dS = entropy change)
U(dU = change in internal energy)
Q(dQ = heat absorbed) (Correct answer)

Correct answer: Q(dQ = heat absorbed)

In thermodynamics, an accurate differential (or exact differential) represents a state function, meaning its value depends only on the initial and final states, not the path taken. Gibbs free energy (G), entropy (S), and internal energy (U) are state functions. However, heat absorbed (Q) is a path function; the amount of heat absorbed depends on the specific process or path taken between two states, making dQ an inexact differential.

Question 16: A tuning fork with a frequency of 450 Hz resonates with a resonance air column that is 40 cm long. Without considering end adjustments, the speed of sound in air is:

720 m/s (Correct answer)
920 m/s
820 m/s
1020 m/s

Correct answer: 720 m/s

For a resonance air column in its fundamental mode (first resonance), the length of the air column (L) is approximately one-quarter of the wavelength (λ/4). Given the length L = 40 cm = 0.4 m, the wavelength λ = 4 * L = 4 * 0.4 m = 1.6 m. The speed of sound (v) is calculated using the formula v = f * λ, where f is the frequency. With f = 450 Hz, v = 450 Hz * 1.6 m = 720 m/s.

Free NEET MCQ Test Questions and Answers

What is true about the following statements?