An organic compound (A) on reduction gave a compound (B). Upon treatment with `HNO_(2)` ,(B) gave ethyl alcohol and on warming with `CHCl_(3)`, and alcoholic KOH, (B ) gave offensive smell. The compound (A) is:

Options

A. `CH_(3)NH_(2)`
B. `CH_(3)NC`
C. `CH_(3)CN`
D. `C_(2)H_(5)CN`

Answer

To solve the problem step by step, we need to analyze the information given in the question and deduce the structure of compound A.

### Step 1: Identify Compound B
The question states that compound A on reduction gives compound B. Furthermore, compound B upon treatment with HNO2 yields ethyl alcohol (C2H5OH). This indicates that compound B is likely a primary amine because primary amines react with nitrous acid (HNO2) to produce alcohols.

**Hint:** Consider the structure of ethyl alcohol to deduce the possible structure of compound B.

### Step 2: Determine the Structure of Compound B
Since ethyl alcohol has 2 carbon atoms, compound B must be a primary amine with 2 carbon atoms. The simplest primary amine that fits this description is ethylamine (C2H5NH2).

**Hint:** Look for amines with the same number of carbon atoms as the alcohol produced.

### Step 3: Analyze the Reaction of Compound B
The question also states that when compound B (ethylamine) is treated with CHCl3 (chloroform) and alcoholic KOH, it produces an offensive smell. This reaction is characteristic of the formation of isocyanides (also known as carbylamines) from primary amines.

**Hint:** Recall that primary amines react with chloroform and alcoholic KOH to form isocyanides.

### Step 4: Identify Compound A
Now, we need to find compound A, which on reduction gives ethylamine (compound B). One possible precursor is acetonitrile (CH3CN). When acetonitrile is reduced, it yields ethylamine.

**Hint:** Think about common organic compounds that can be reduced to form primary amines.

### Step 5: Write the Reactions
1. **Reduction of Acetonitrile:**
\[ \text{CH}_3\text{CN} + \text{H}_2 \rightarrow \text{C}_2\text{H}_5\text{NH}_2 \quad (\text{Ethylamine}) \]

2. **Reaction of Ethylamine with HNO2:**
\[ \text{C}_2\text{H}_5\text{NH}_2 + \text{HNO}_2 \rightarrow \text{C}_2\text{H}_5\text{OH} + \text{N}_2 + \text{H}_2\text{O} \]

3. **Formation of Isocyanide:**
\[ \text{C}_2\text{H}_5\text{NH}_2 + \text{CHCl}_3 + \text{KOH} \rightarrow \text{C}_2\text{H}_5\text{NC} + \text{KCl} + \text{H}_2\text{O} \]

### Conclusion
Based on the deductions made, the compound A is acetonitrile (CH3CN).

**Final Answer:** The compound A is **acetonitrile (CH3CN)**.

---