A metal oxide (such as ZnO, CuO) reacts with an acid to give to give the respective salt and water as by products.
Here, Consider the examples given below:
1) Zinc oxide reacts with hydrochloric acid:
ZnO (s) + 2HCl (aq) -->ZnCl2 (aq) + H2O
2) Copper oxide reacts with hydrochloric acid:
CuO (s) + 2HCl (aq) -->CuCl2 (aq) + H2O
