Question

the lock-and-key mechanism refers to
the complementary shapes of an enzyme and a substrate.
the attractive forces between an enzyme and a substrate.
the ability of an enzyme to lower the activation energy of a reaction.
the ability of an enzyme to \unlock\ the products of a reaction.

Explanation:

The lock - and - key model of enzyme - substrate interaction proposes that the active site of an enzyme (the "lock") has a specific three - dimensional shape that is complementary to the shape of the substrate (the "key"). This complementary shape allows the substrate to fit precisely into the enzyme's active site. The option about attractive forces is incorrect as the lock - and - key model is about shape complementarity, not just forces. The ability of an enzyme to lower activation energy is a general property of enzymes related to catalysis, not the lock - and - key mechanism. And enzymes do not "unlock" products; they facilitate the conversion of substrates to products.

Answer:

the complementary shapes of an enzyme and a substrate.