Neet 2019 Chemistry Question (31-45)

Q31. Which of the following does not contain a coordinate bond?

A. NH₄⁺
B. H₃O⁺
C. BF₃
D. CO

Answer: C

Comment: In BF₃, all bonds are covalent. No lone pair donation occurs.

Explanation: NH₄⁺, H₃O⁺, and CO involve lone pair donation (coordinate bond), but BF₃ does not.

Q32. The basicity of aniline is less than ammonia due to:

A. Inductive effect
B. Mesomeric effect
C. Hyperconjugation
D. Steric effect

Answer: B

Comment: Lone pair on nitrogen in aniline is delocalized with benzene ring.

Explanation: Mesomeric (resonance) effect reduces availability of lone pair for protonation.

Q33. Which of the following molecules shows resonance?

A. C₂H₆
B. CO₃²⁻
C. CH₄
D. C₂H₂

Answer: B

Comment: Carbonate ion has delocalized electrons over 3 oxygen atoms.

Explanation: Resonance structures involve delocalized pi electrons in conjugated systems like CO₃²⁻.

Q34. Which of the following is aromatic?

A. Cyclooctatetraene
B. Benzene
C. Cyclobutadiene
D. Cyclopentadiene

Answer: B

Comment: Benzene follows Huckel's rule (4n + 2 π electrons).

Explanation: Benzene is cyclic, planar, and has 6 π electrons, making it aromatic.

Q35. Which has highest ionization energy?

A. Na
B. Mg
C. Al
D. Cl

Answer: D

Comment: Ionization energy increases across a period.

Explanation: Cl has highest nuclear charge and smallest size among the options.

Q36. Which one is most reactive towards electrophilic substitution?

A. Toluene
B. Nitrobenzene
C. Benzoic acid
D. Benzaldehyde

Answer: A

Comment: Toluene has an electron-donating methyl group.

Explanation: Activating groups like –CH₃ increase reactivity in electrophilic substitution.

Q37. Which of the following is most stable carbocation?

A. CH₃⁺
B. CH₃CH₂⁺
C. (CH₃)₃C⁺
D. CH₂=CH–CH₂⁺

Answer: C

Comment: More alkyl groups stabilize the carbocation via hyperconjugation.

Explanation: Tertiary carbocation (CH₃)₃C⁺ is most stable due to inductive and hyperconjugation effects.

Q38. Which acid has the lowest pKa value?

A. Acetic acid
B. Formic acid
C. Benzoic acid
D. Chloroacetic acid

Answer: D

Comment: Electron withdrawing Cl increases acidity.

Explanation: More acidic = lower pKa. Chloro group stabilizes the conjugate base.

Q39. Which gives a white precipitate with AgNO₃?

A. CH₃Br
B. CH₃CH₂Cl
C. C₂H₅OH
D. CH₃CH₂I

Answer: B

Comment: AgNO₃ reacts with alkyl halides forming silver halide ppt.

Explanation: CH₃CH₂Cl forms white ppt of AgCl with AgNO₃ in ethanol.

Q40. What is the product of Cannizzaro reaction?

A. Ester
B. Aldehyde
C. Alcohol + Carboxylic acid
D. Alcohol + Salt of acid

Answer: D

Comment: Disproportionation of non-enolizable aldehydes.

Explanation: One aldehyde is oxidized to salt, other reduced to alcohol.

Q41. Which of the following is amphoteric?

A. Na₂O
B. MgO
C. Al₂O₃
D. SiO₂

Answer: C

Comment: Amphoteric oxides react with both acids and bases.

Explanation: Al₂O₃ reacts with HCl and NaOH → amphoteric.

Q42. Which of the following contains no unpaired electron?

A. Cu²⁺
B. Fe²⁺
C. Zn²⁺
D. Mn²⁺

Answer: C

Comment: Zn²⁺ has 3d¹⁰ configuration.

Explanation: Completely filled d-orbitals → no unpaired electrons.

Q43. Which of the following is used in photosynthesis?

A. CO₂
B. CO
C. NO₂
D. SO₂

Answer: A

Comment: Plants use CO₂ to synthesize glucose in presence of sunlight.

Explanation: CO₂ is the primary carbon source for plants.

Q44. Which of the following is paramagnetic?

A. O₂
B. N₂
C. H₂
D. CO

Answer: A

Comment: O₂ has two unpaired electrons in molecular orbital theory.

Explanation: Paramagnetic = unpaired electrons. O₂ fits this via MO theory.

Q45. Which compound has sp³ hybridization on central atom?

A. CO₂
B. BF₃
C. NH₃
D. SO₂

Answer: C

Comment: NH₃ has 3 sigma bonds + 1 lone pair → sp³ hybridized.

Explanation: 4 regions of electron density → sp³ hybridization.