The antiknock agent added to unleaded petrol is

Options

A. tetraethyl lead
B. tetramethly lead
C. dibromoethane
D. methyltertiary butyl ether

Answer

### Step-by-Step Solution

1. **Understanding Anti-Knock Agents**:
- Anti-knock agents are substances added to fuels to prevent knocking, which is an undesirable sound produced by uneven combustion in an engine. Knocking can damage the engine and reduce its efficiency.

2. **Identifying the Purpose of Anti-Knock Agents**:
- The primary function of an anti-knock agent is to ensure that fuel burns evenly and efficiently, thereby reducing engine noise and preventing damage. Additionally, they help in reducing harmful emissions like carbon monoxide.

3. **Exploring Unleaded Petrol**:
- Unleaded petrol is a type of gasoline that does not contain lead, which is a harmful pollutant. This makes it more environmentally friendly compared to leaded petrol.

4. **Evaluating the Options**:
- **Option 1: Tetraethyl Lead**: This is a known anti-knock agent but is not used in unleaded petrol due to its toxicity and environmental impact.
- **Option 2: Tetramethyl Lead**: Similar to tetraethyl lead, this compound is harmful and not used as an anti-knock agent.
- **Option 3: Dibromoethane**: This compound releases corrosive gases upon combustion and is not suitable as an anti-knock agent.
- **Option 4: Methyl Tertiary Butyl Ether (MTBE)**: This compound is used in unleaded petrol as it increases the octane number (the fuel's ability to resist knocking) and enhances oxygen content, leading to more efficient combustion.

5. **Conclusion**:
- Based on the evaluation of the options, the correct answer is **Methyl Tertiary Butyl Ether (MTBE)**, as it is the anti-knock agent added to unleaded petrol.

### Final Answer
The anti-knock agent added to unleaded petrol is **Methyl Tertiary Butyl Ether (MTBE)**.

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