Which of the following is not a property of hydrogen ?

Options

A. It is a colourless, odourless gas
B. It is highly combustible.
C. It is highly poisonous gas
D. It is lighter than air.

Explanation

To determine which of the following is not a property of hydrogen, we will analyze each option provided:

1. **Colorless and Odorless Gas**:
- Hydrogen is indeed a colorless and odorless gas. This is a true property of hydrogen.

2. **Highly Combustible**:
- Hydrogen is known for its high combustibility. It reacts readily with oxygen to form water, releasing a significant amount of energy in the process. This is also a true property of hydrogen.

3. **Highly Poisonous Gas**:
- This statement is false. Hydrogen is not a poisonous gas; in fact, it is considered non-toxic. Therefore, this is not a property of hydrogen.

4. **Lighter than Air**:
- Hydrogen is lighter than air, which is another true property. It has a lower density compared to air.

From the analysis above, the only statement that is not a property of hydrogen is that it is a "highly poisonous gas."

**Final Answer**: C) Highly Poisonous Gas

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