What is the action of Zn-Hg in conc. HCl on acetaldehyde?

Explanation

### Step-by-Step Solution:

1. **Identify the Reactants**:
The reactants in this reaction are acetaldehyde (C2H4O) and the reducing agent zinc amalgam (Zn-Hg) in the presence of concentrated hydrochloric acid (HCl).

2. **Understand the Reaction Type**:
The reaction of acetaldehyde with Zn-Hg in concentrated HCl is known as the Clemenson reduction. This reaction is used to reduce carbonyl compounds (like aldehydes and ketones) to alkanes.

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