NEET Chemistry 5 — Questions and Answers
Question 1: Which of the following reagents converts a primary alcohol to an aldehyde without further oxidation to a carboxylic acid?
- KMnO₄/H₂SO₄
- K₂Cr₂O₇/H₂SO₄
- PCC (pyridinium chlorochromate) (Correct answer)
- Concentrated HNO₃
Correct answer: PCC (pyridinium chlorochromate)
PCC (pyridinium chlorochromate) is a mild oxidizing agent that oxidizes primary alcohols to aldehydes and stops there without forming carboxylic acids.
Question 2: The crystal field splitting energy (Δo) is largest for which of the following ligands?
- F⁻
- H₂O
- NH₃
- CN⁻ (Correct answer)
Correct answer: CN⁻
CN⁻ is a strong-field ligand at the top of the spectrochemical series, producing the largest crystal field splitting energy Δo.
Question 3: In electrolysis of dilute H₂SO₄ solution, what is produced at the anode?
- Hydrogen gas
- Oxygen gas (Correct answer)
- Sulphur dioxide
- Sulphuric acid
Correct answer: Oxygen gas
At the anode, water is oxidized (2H₂O → O₂ + 4H⁺ + 4e⁻) in dilute H₂SO₄ because O₂ is discharged in preference to SO₄²⁻.
Question 4: Nylon-6 is produced by the polymerization of:
- Caprolactam (Correct answer)
- Hexamethylenediamine and adipic acid
- ε-aminocaproic acid only by condensation
- Phenol and formaldehyde
Correct answer: Caprolactam
Nylon-6 is produced by the ring-opening polymerization of caprolactam (a cyclic amide with 6 carbon atoms).
Question 5: Which of the following is the correct IUPAC name for [Co(NH₃)₄Cl₂]Cl?
- Dichlorotetramminecobalt(II) chloride
- Tetraamminedichlorocobalt(III) chloride (Correct answer)
- Tetramminedichloro cobaltate(III) chloride
- Dichlorotetramine cobalt(III) chloride
Correct answer: Tetraamminedichlorocobalt(III) chloride
In IUPAC nomenclature for coordination compounds, ligands are listed alphabetically (ammine before chloro), followed by the metal and its oxidation state, then the outer sphere ion.
Question 6: Which of the following statements about entropy is correct?
- Entropy decreases when a gas is dissolved in a liquid (Correct answer)
- Entropy of a crystalline solid at 0 K is always positive
- Entropy always increases in spontaneous reactions
- Entropy change is zero for all isothermal processes
Correct answer: Entropy decreases when a gas is dissolved in a liquid
When a gas dissolves in a liquid, the ordered arrangement increases (gas randomness is lost), so entropy decreases.
Question 7: Which of the following is an example of a Cannizzaro reaction?
- CH₃CHO + NaOH → CH₃COONa + CH₃OH
- HCHO + NaOH → HCOONa + CH₃OH
- CH₃COCH₃ + NaOH → CH₃COO⁻ + CH₃OH
- C₆H₅CHO + NaOH → C₆H₅COO⁻ + C₆H₅CH₂OH (Correct answer)
Correct answer: C₆H₅CHO + NaOH → C₆H₅COO⁻ + C₆H₅CH₂OH
Benzaldehyde (no α-hydrogen) undergoes Cannizzaro reaction with NaOH: one molecule is oxidized to benzoate and another is reduced to benzyl alcohol.
NEET Chemistry 5
Which of the following reagents converts a primary alcohol to an aldehyde without further oxidation to a carboxylic acid?