Which one of the following substances react with nitrous acid to give a hydroxy compound?

Options

A. `C_2H_5NH_2`
B. `(C_2H_5)_(2)NH`
C. `C_6H_5NH_2`
D. Both (a) and (c)

Explanation

To solve the question of which substance reacts with nitrous acid (HNO2) to give a hydroxy compound, we will analyze the reactions of different types of amines with nitrous acid.

### Step-by-Step Solution:

1. **Identify the Types of Amines:**
- The substances in question are likely to be primary amines, secondary amines, and possibly anilines (aromatic amines).

2. **Reaction of Primary Amines with Nitrous Acid:**
- A primary amine (e.g., CH3-CH2-NH2) reacts with nitrous acid at low temperatures (around 273-278 K).
- The reaction produces a hydroxy compound (alcohol) and nitrogen gas (N2).
- For example:
\[ \text{CH}_3\text{CH}_2\text{NH}_2 + \text{HNO}_2 \rightarrow \text{CH}_3\text{CH}_2\text{OH} + \text{N}_2 + \text{H}_2\text{O} \]
- Here, ethanol (CH3CH2OH) is formed, which is a hydroxy compound.

3. **Reaction of Secondary Amines with Nitrous Acid:**
- A secondary amine (e.g., CH3-CH(NH2)-CH3) reacts with nitrous acid at low temperatures (0-5 °C).
- The product is a nitroso compound, which does not contain a hydroxy group. Instead, it forms a yellow oily nitrous amine.
- For example:
\[ \text{C}_2\text{H}_5\text{NH}_2 + \text{HNO}_2 \rightarrow \text{C}_2\text{H}_5\text{N}=\text{N}^+\text{O}^- + \text{H}_2\text{O} \]
- No hydroxy compound is formed in this case.

4. **Reaction of Anilines with Nitrous Acid:**
- An aniline (e.g., C6H5-NH2) also reacts with nitrous acid at low temperatures (0-5 °C).
- The reaction produces a diazonium salt (C6H5-N2^+Cl^-) and does not yield a hydroxy compound.
- For example:
\[ \text{C}_6\text{H}_5\text{NH}_2 + \text{HNO}_2 \rightarrow \text{C}_6\text{H}_5\text{N}_2^+ + \text{Cl}^- + \text{H}_2\text{O} \]
- Again, no hydroxy compound is formed.

5. **Conclusion:**
- Among the options, only the primary amine reacts with nitrous acid to produce a hydroxy compound. Therefore, the correct answer is the primary amine.

### Final Answer:
The substance that reacts with nitrous acid to give a hydroxy compound is **primary amine**.