Which of the following is a property of hydrogen?

Options

A. colourless and pungent
B. acidic gas
C. supports combustion
D. reducing agent

Answer

To determine which of the following is a property of hydrogen, we will evaluate each option provided:

1. **Colorless and Pungent**:
- Hydrogen is indeed a colorless gas; however, it is not pungent. In fact, hydrogen is an odorless gas. Therefore, this statement is incorrect.

2. **Acidic Gas**:
- Hydrogen gas is neither acidic nor basic; it is considered a neutral gas. Thus, this statement is also incorrect.

3. **Supports Combustion**:
- Hydrogen does not support combustion in the way that oxygen does. Instead, it can combust when mixed with oxygen, but it does not support combustion by itself. Therefore, this statement is incorrect as well.

4. **Reducing Agent**:
- Hydrogen acts as a reducing agent. When hydrogen gas passes over metallic oxides, it can remove oxygen from these oxides, thereby reducing them to their corresponding metals. For example, when hydrogen reacts with copper oxide (CuO), it reduces it to copper (Cu) and water (H2O). This process demonstrates that hydrogen is indeed a reducing agent.

Based on the evaluation of the options, the correct property of hydrogen is that it is a **reducing agent**.

### Final Answer:
The property of hydrogen that is true is that it is a **reducing agent**.