A colourless organic compound gives brisk effervescence with a mixture of sodium nitrite and dil. `HCl`. It could be

Options

A. Oxalic acid
B. Acetic acid
C. Urea
D. Glucose

Answer

To solve the question, we need to identify the organic compound that gives brisk effervescence when reacted with a mixture of sodium nitrite (NaNO2) and dilute hydrochloric acid (HCl).

### Step-by-Step Solution:

1. **Understanding the Reaction**:
When sodium nitrite (NaNO2) is mixed with dilute hydrochloric acid (HCl), it generates nitrous acid (HNO2). The reaction can be represented as:
\[ \text{NaNO}_2 + \text{HCl} \rightarrow \text{HNO}_2 + \text{NaCl} \]

2. **Identifying the Organic Compound**:
The organic compound in question must be capable of reacting with nitrous acid (HNO2) to produce gases that cause brisk effervescence. A well-known compound that reacts with HNO2 is urea (H2NCONH2).

3. **Reaction of Urea with HNO2**:
When urea reacts with nitrous acid, it undergoes decomposition, producing carbon dioxide (CO2), ammonia (NH3), water (H2O), and nitrogen gas (N2). The reaction can be summarized as:
\[ \text{H}_2\text{NCONH}_2 + \text{HNO}_2 \rightarrow \text{CO}_2 + \text{NH}_3 + \text{H}_2\text{O} + \text{N}_2 \]
The production of gases like CO2 and N2 is what leads to the brisk effervescence observed.

4. **Conclusion**:
Based on the above reactions and the fact that urea is a colorless organic compound, we can conclude that the compound that gives brisk effervescence with a mixture of sodium nitrite and dilute HCl is urea.

### Final Answer:
The colorless organic compound is **urea (H2NCONH2)**.