When a metal oxide reacts with an acid, it undergoes a chemical reaction called acid-base reaction or neutralization reaction. The products formed in this reaction are salt and water.

The general chemical equation for this reaction can be represented as:

Metal Oxide (MO) + Acid (HX) → Salt (MX) + Water (H2O)

For example, when Calcium Oxide (CaO) reacts with Hydrochloric Acid (HCl), it produces Calcium Chloride (CaCl2) and water:

CaO(s) + 2HCl(aq) → CaCl2 (aq) + H2O(l)

In this reaction, Calcium Oxide (CaO) is the metal oxide, Hydrochloric Acid (HCl) is the acid, Calcium Chloride (CaCl2) is the salt, and Water (H2O) is the byproduct.