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Steel, composed of carbon and iron, is an example of an interstitial alloy.
Which of the following choices represents the BEST explanation for the fact that steel is harder and stronger than pure iron?
Carbon atoms are more reactive with oxygen than iron atoms. This prevents the steel from forming rust.
Carbon atoms are smaller than iron atoms. Carbon atoms fill the spaces between iron atoms, making the structure more rigid.
Carbon atoms form strong bonds with other carbon atoms. This forms a protective layer on the surface of steel.
Both carbon and iron are good conductors of electricity. This makes steel harder and stronger than pure iron.