Here's why:

* Metal oxides are basic in nature. They react with acids to form salts and water.

* Hydrochloric acid (HCl) is a strong acid.

* The reaction: The metal oxide reacts with the hydrochloric acid to form a metal chloride salt and water.

Here's a general equation:

Metal oxide + Hydrochloric acid → Metal chloride + Water

Example:

CuO (copper oxide) + 2HCl (hydrochloric acid) → CuCl₂ (copper chloride) + H₂O (water)

This reaction is characterized by the release of heat, indicating an exothermic process.