An unknown aldehyde [A] on reacting with alkali gives `beta`-hydroxyaldehyde which loses water to form an unsaturated but-2-enal. Another aldehyde [B] undergoes disproportionation reaction in the presence of conc. Alkali to form products [C] and [D]. The compound [C] is an aryl alcohol with formula `C_(7)H_(8)O`.
(i) Identify [A] to [B]. , (ii) Write the sequence of reactions involved.
(iii) Name the proucts when , [B] reacts with zinc amalgam and hydrochloric acid.

Explanation

To solve the problem step by step, let's break down the information provided in the question and the video transcript.

### Step 1: Identify Aldehyde [A]
The unknown aldehyde [A] reacts with alkali to form a beta-hydroxyaldehyde, which then loses water to form an unsaturated but-2-enal.

1. **Aldehyde [A]**: Since the reaction involves forming a beta-hydroxyaldehyde and subsequently but-2-enal, we can deduce that [A] is likely to be acetaldehyde (CH3CHO).
2. **Reaction with NaOH**:
- When acetaldehyde reacts with NaOH, it undergoes aldol condensation to form 3-hydroxybutanal (the beta-hydroxyaldehyde).
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