How is a salt formed from an acid and a metal according to the given description?

• A. Hydrogen in the acid is replaced by a metal
• B. A metal displaces water
• C. The acid is oxidized
• D. The metal reduces the acid

Answer: (A)

When a salt forms from an acid and a metal, a displacement reaction occurs: a more reactive metal pushes out the hydrogen from the acid, so the metal combines with the acid’s anion to make a salt and hydrogen gas is released. This is why the statement that hydrogen in the acid is replaced by a metal best describes the process. For example, zinc reacting with hydrochloric acid gives zinc chloride and hydrogen gas: Zn + 2 HCl → ZnCl2 + H2.

Displacing water would be a different type of reaction, and in this case the acid is not being oxidized; instead hydrogen ions are reduced to hydrogen gas while the metal is oxidized. Saying the metal reduces the acid is imprecise—the key idea is that the hydrogen is replaced by the metal to form the salt.