A white solid X reacts with dil. HCl to give colourless gas which is used in fire extinguishers. The solid X is

Options

A. NaCl
B. `CH_(3)COONa`
C. `Na_(2)CO_(3)`
D. `NaHCO_(3)`

Explanation

To solve the question, we need to identify a white solid (X) that reacts with dilute hydrochloric acid (HCl) to produce a colorless gas, which is known to be used in fire extinguishers.

### Step-by-Step Solution:

1. **Identify the Reaction**: We need to find a solid that reacts with dilute HCl to produce a gas. The gas produced should be colorless and used in fire extinguishers.

2. **Consider Common Reactions**: One common reaction that produces a gas when a solid reacts with an acid is the reaction of carbonates or bicarbonates with acids.

3. **Identify the Gas**: The gas that is commonly used in fire extinguishers is carbon dioxide (CO2). Therefore, we need a solid that can produce CO2 when it reacts with HCl.

4. **Choose the Solid**: Sodium bicarbonate (NaHCO3), also known as sodium hydrogen carbonate, is a white solid that reacts with dilute hydrochloric acid to produce sodium chloride (NaCl), water (H2O), and carbon dioxide (CO2). The reaction is as follows:
\[ \text{NaHCO}_3 (s) + \text{HCl} (aq) \rightarrow \text{NaCl} (aq) + \text{CO}_2 (g) + \text{H}_2\text{O} (l) \]

5. **Confirm the Properties**: Sodium bicarbonate is indeed a white solid and produces a colorless gas (CO2) when it reacts with dilute HCl, which is used in fire extinguishers.

### Conclusion:
The solid X is sodium bicarbonate (NaHCO3).

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