Tetraethyl lead is added to aviation gasoline to

• A. Reduce engine wear
• B. Increase octane rating
• C. Lower volatility
• D. Improve the gasoline's performance in the engine

Answer: (D)

Tetraethyl lead raises the gasoline’s resistance to knocking, which means the fuel can tolerate higher compression without detonating. When an engine runs without knocking, it can develop more peak power and run more smoothly, especially under demanding flight conditions. That clearer, more robust performance is the direct result of increasing the fuel’s octane rating, so describing the purpose as improving the engine’s performance captures the actual outcome of adding TEL. While TEL also provides some lubrication for valve seats, the key reason it’s added is to prevent detonation and enable stronger, more efficient operation, which is why the overall statement about improving engine performance best describes its purpose.