A gas which is combustible and can support combustion is.

Options

A. oxygen.
B. nitrous oxide.
C. nitric oxide.
D. carbon monoxide.

Answer

To solve the question "A gas which is combustible and can support combustion is," we need to analyze the properties of the gases provided in the options. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Terms
- **Combustible**: A gas that can burn itself.
- **Supports Combustion**: A gas that helps other substances to burn but does not necessarily burn itself.

### Step 2: Analyze Each Gas Option
1. **Oxygen (O₂)**:
- **Combustible**: No, it does not burn itself.
- **Supports Combustion**: Yes, it supports the burning of other substances.
- **Conclusion**: Not the correct answer.

2. **Nitrous Oxide (N₂O)**:
- **Combustible**: Yes, it can burn itself.
- **Supports Combustion**: Yes, it supports combustion.
- **Conclusion**: This is a correct answer.

3. **Nitric Oxide (NO)**:
- **Combustible**: Yes, it can burn itself.
- **Supports Combustion**: Yes, it supports combustion.
- **Conclusion**: This is also a correct answer.

4. **Carbon Monoxide (CO)**:
- **Combustible**: No, it does not burn itself.
- **Supports Combustion**: Yes, it supports the burning of other substances.
- **Conclusion**: Not the correct answer.

### Step 3: Final Conclusion
- The gases that are both combustible and can support combustion are **Nitrous Oxide (N₂O)** and **Nitric Oxide (NO)**.

### Answer:
The gases which are combustible and can support combustion are **Nitrous Oxide (N₂O)** and **Nitric Oxide (NO)**.

---