The propery which distinguishes fomric acid from acetic acid is

Options

A. only ammonium salt of formic acid on heating gives amide
B. when heated with `"alcohol"//H_(2)SO_(4)`, only acetic acid fomrs ester
C. only acetic forms salts with alkali
D. only formic reduces Fehling's solution

Explanation

To distinguish formic acid (HCOOH) from acetic acid (CH3COOH), we need to analyze their chemical properties. Here’s a step-by-step solution to identify the distinguishing property:

### Step 1: Identify the Structures
- Formic acid (HCOOH) has the structure:
\[ \text{H} - \text{C}(=O) - \text{OH} \]
- Acetic acid (CH3COOH) has the structure:
\[ \text{CH}_3 - \text{C}(=O) - \text{OH} \]

### Step 2: Analyze the Properties
- Both acids are carboxylic acids and share similar functional groups, but their reactivity can differ due to the presence of different substituents (hydrogen in formic acid and a methyl group in acetic acid).

### Step 3: Evaluate the Options
1. **Ammonium Salt Formation**: Both acids can form ammonium salts, so this does not distinguish them.
2. **Reaction with Alcohol in Acidic Medium**: Both acids can react with alcohols to form esters, so this also does not distinguish them.
3. **Salt Formation with Alkali**: Both acids will form salts with alkalis, so this is not a distinguishing property.
4. **Reaction with Fehling’s Solution**: Formic acid can reduce Fehling’s solution (Cu²⁺ ions), resulting in the formation of a red precipitate of Cu₂O. Acetic acid does not have this property and will not reduce Fehling’s solution.

### Conclusion
The property that distinguishes formic acid from acetic acid is that **only formic acid reduces Fehling's solution**. Therefore, the correct answer is:

**Option D: Only formic acid reduces Fehling's solution.**

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