Give the formulae of [A] and [B]
`CH_(3)CH_(2)MgBr+CO_(2)overset((i)"Dry ether")underset((ii)H^(+)//H_(2)O)rarr[A]overset(PCl_(5))rarr[B]`

Explanation

To solve the question, we will go through the steps of the reaction involving the Grignard reagent, carbon dioxide, and phosphorus pentachloride.

### Step-by-Step Solution:

1. **Identify the Grignard Reagent**: The given Grignard reagent is CH₃CH₂MgBr (ethylmagnesium bromide). Grignard reagents react with carbon dioxide to form carboxylic acids.

2. **Reaction with Carbon Dioxide**:
- When CH₃CH₂MgBr reacts with CO₂ in the presence of dry ether, it forms a carboxylate intermediate. The carbon dioxide acts as an electrophile and the Grignard reagent acts as a nucleophile.
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