Which of the following is used as an ‘anti-knock’ in automobile engines? automobile engines?

Explanation

Knocking is a problem that occurs in petrol engines when the fuel-air mixture ignites too early or unevenly in the engine cylinder. This causes a rattling or knocking sound and can damage the engine over time. It happens because some fuels burn too quickly or at the wrong moment.

Lead tetra-ethyl, also written as Pb(C₂H₅)₄ or tetraethyl lead (TEL), was the most widely used anti-knock agent. When added to petrol in small amounts, it slows down the combustion of fuel so that it burns smoothly and evenly rather than exploding suddenly. This prevents the knocking sound and protects the engine.

However, lead tetra-ethyl releases lead compounds into the air when the fuel burns. Lead is a toxic heavy metal that causes serious health problems including brain damage, especially in children. Because of this, most countries have now banned leaded petrol and switched to unleaded fuel with other anti-knock additives.

Tetramethyl silane is used as a reference compound in NMR spectroscopy, not as a fuel additive. Glycerol is a thick, sweet liquid used in food and cosmetics. N-heptane actually has a very low octane rating and is used as a standard for measuring how easily a fuel knocks, so it would increase knocking, not prevent it.