What describes a fuel sample's ability to resist knock and ping?

The ability of a fuel sample to resist knock and ping is referred to as its octane rating. This is a critical characteristic for gasoline, particularly in high-compression engines where fuel is subjected to higher pressures and temperatures, potentially leading to premature ignition or knocking. The octane rating indicates the fuel's ability to withstand compression without detonating. A higher octane rating means greater resistance to knock, resulting in smoother engine operation and increased performance. Thus, fuels with high octane ratings can safely be used in engines designed for performance, where the risk of engine knock is higher.

While the other options pertain to fuel properties, they do not relate directly to resistance to knock. Cetane, for instance, is related to diesel fuel performance, heptane is often used as a reference in discussing lower octane ratings, and stoichiometry refers to the ratios of reactants and products in chemical reactions, not specifically related to fuel knock resistance.