Which of the following is used as an anti-knocking material ?

Options

A. Glyoxal
B. Freon
C. T.E.L.
D. Ethyl alcohol

Answer

### Step-by-Step Solution:

1. **Understanding Anti-Knocking Agents**:
- Anti-knocking agents are additives used in gasoline to reduce engine knocking. Knocking occurs when fuel ignites prematurely in the engine cylinder, which can cause damage and reduce efficiency.

2. **Function of Anti-Knocking Agents**:
- These agents help to increase the octane rating of the fuel. The octane rating measures a fuel's ability to resist knocking during combustion. A higher octane rating means better performance and efficiency.

3. **Mechanism of Action**:
- Anti-knocking agents work by raising the temperature and pressure at which ignition occurs. This means that the fuel will ignite more efficiently and at the right time, thus reducing the chances of knocking.

4. **Identifying the Anti-Knocking Agent**:
- Among the options provided, we need to identify which substance acts as an anti-knocking agent. The most commonly known anti-knocking agent is tetraethyl lead (TEL).

5. **Conclusion**:
- Therefore, the correct answer to the question "Which of the following is used as an anti-knocking material?" is **tetraethyl lead (TEL)**, which is found in option C.