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Fuel additives: inhibitor of pre-ignition/knock in spark-ignition engines Identify the effective inhibitor historically used to suppress pre-ignition/knock. Choose the correct option.

Difficulty: Easy

Alcohol
Water
Lead
None of these

Correct Answer: Lead

Explanation:

Concept
Tetraethyl lead (TEL) was historically used to raise octane number and reduce knock/pre-ignition in petrol engines by slowing end-gas reactions. (Modern fuels use unleaded additives due to environmental regulations.)

Notes
Alcohol/water injection can reduce charge temperature and suppress knock in specific setups but TEL was the classic chemical inhibitor.

Final Answer
Lead

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