This gas burns with a popping sound.

Options

A. Oxygen
B. Nitrogen
C. Hydrogen
D. Chlorine

Explanation

### Step-by-Step Solution:

1. **Identify the Gas**: The question states that a gas burns with a popping sound. The gas in question is hydrogen.

2. **Understanding the Reaction**: When hydrogen gas is exposed to a flame (like that of a burning candle), it reacts with oxygen in the air. This reaction is highly exothermic, meaning it releases a lot of energy in the form of heat and light.

3. **Popping Sound Explanation**: The popping sound occurs because hydrogen gas forms an explosive mixture with air. When this mixture is ignited, it produces a rapid expansion of gases, which creates the characteristic popping sound.

4. **Conditions for the Sound**: If the amount of air (oxygen) in the mixture is limited, the explosion is not dangerous, and the hydrogen burns with a distinct popping sound instead of a loud explosion.

5. **Conclusion**: Therefore, the gas that burns with a popping sound is hydrogen gas.

### Final Answer:
The gas that burns with a popping sound is **hydrogen gas**.

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