The reagent used to convert `RCOOH rarr RCH_(2)OH` is

Options

A. `NaBH_(4)`
B. Na/Alcohol
C. Zn/Hg-HCl
D. `LiAIH_(4)`

Explanation

To convert a carboxylic acid (RCOOH) to a primary alcohol (RCH2OH), we need to use a suitable reducing agent. Let's break down the steps to find the correct reagent for this reaction.

### Step-by-Step Solution:

1. **Identify the Reaction Type**:
- The conversion of RCOOH to RCH2OH involves the reduction of a carboxylic acid to a primary alcohol. This is a reduction reaction where the carbonyl group (C=O) in the carboxylic acid is reduced to a hydroxyl group (–OH) in the alcohol.

**Hint**: Remember that reduction involves the gain of electrons or hydrogen, or the loss of oxygen.

2. **Determine the Required Reducing Agent**:
- For the reduction of carboxylic acids to alcohols, a strong reducing agent is typically required.

**Hint**: Consider the strength of the reducing agents provided in the options.

3. **Evaluate the Options**:
- **Option A: NaBH4 (Sodium Borohydride)**: This is a mild reducing agent, effective for aldehydes and ketones but not strong enough for carboxylic acids.
- **Option B: Sodium in Alcohol**: This can act as a reducing agent but is not commonly used for this specific transformation.
- **Option C: Zinc, Hg, HCl**: This combination does not serve as a reducing agent for carboxylic acids.
- **Option D: LiAlH4 (Lithium Aluminum Hydride)**: This is a strong reducing agent capable of reducing carboxylic acids to primary alcohols.

**Hint**: Compare the effectiveness of each reagent based on their reducing strength.

4. **Select the Correct Reagent**:
- Based on the evaluation, LiAlH4 (Option D) is the most suitable reagent for converting RCOOH to RCH2OH.

**Hint**: Strong reducing agents like LiAlH4 are often necessary for the reduction of more stable functional groups like carboxylic acids.

### Final Answer:
The reagent used to convert RCOOH to RCH2OH is **LiAlH4 (Lithium Aluminum Hydride)**.