Q. The correct order of acidic strength of the major products formed in the given reactions, is :

A. PhNH₂ → (1) NaNO₂ + HCl (< 5°C) → (2) CuCN → (3) H₃O⁺ / Δ → [A]

B. CH₃CH₂CHO → [Ag(NH₃)₂]⁺, OH⁻, Δ → [B]

C. CH₄ + O₂ → (i) Mo₂O₃ → (ii) Na₂Cr₂O₇ / H⁺ → [C]

D. PhCH₂MgBr + CO₂ → Dry ether → H₃O⁺ → [D]

Choose the correct answer from the options given below :

Correct Answer: C > A > D > B

Explanation

First, identify the major products formed in each reaction.

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Reaction A

Aniline (PhNH₂) undergoes diazotisation with NaNO₂/HCl at low temperature to form benzene diazonium chloride.

On treatment with CuCN (Sandmeyer reaction), it forms benzonitrile (PhCN).

Acidic hydrolysis of nitrile gives benzoic acid (C₆H₅COOH).

So, product [A] = Benzoic acid.

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Reaction B

CH₃CH₂CHO (propanal) with Tollens’ reagent is oxidised to propanoic acid (CH₃CH₂COOH).

So, product [B] = Propanoic acid.

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Reaction C

Controlled oxidation of methane using Mo₂O₃ followed by strong oxidation with Na₂Cr₂O₇/H⁺ gives carbonic acid (H₂CO₃).

So, product [C] = Carbonic acid.

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Reaction D

Grignard reagent PhCH₂MgBr reacts with CO₂ followed by acidic workup to give phenylacetic acid (C₆H₅CH₂COOH).

So, product [D] = Phenylacetic acid.

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Now compare acidic strength:

Carbonic acid is strongest due to inorganic nature and high polarity.

Benzoic acid is stronger than phenylacetic acid due to resonance stabilisation of its conjugate base.

Propanoic acid is the weakest among these.

Therefore, the correct order is:

C > A > D > B

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