On cooling acetaldehyde with a few drops of conc. `H_2 SO_4` at `0^@ C,` the product formed is paraldehyde/metaldehyde.

Explanation

To solve the question regarding the product formed when acetaldehyde is cooled with concentrated sulfuric acid, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactant in this case is acetaldehyde, which has the molecular formula \( \text{CH}_3\text{CHO} \).

2. **Understand the Reaction Conditions**: We are cooling acetaldehyde with a few drops of concentrated sulfuric acid (\( \text{H}_2\text{SO}_4 \)) at \( 0^\circ C \). Concentrated sulfuric acid acts as a dehydrating agent.

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