i. When hydrochloric acid reacts with sodium carbonate the following reactions takes place : -

Na₂CO₃(s) + 2HCl (aq) → 2NaCl(s) + H₂O (l) + CO₂ (g)

Hence, when an acid reacts with a metal carbonate the corresponding salt is formed along with the evolution of carbon dioxide gas and the formation of water.

ii. When hydrochloric acid reacts with sodium hydrogen carbonate the following reactions takes place : -

NaHCO₃(s) + HCl (aq) → NaCl(s) + H₂O (l) + CO₂ (g)

Hence, when an acid reacts with a metal hydrogen carbonate the corresponding salt is formed along with the evolution of carbon dioxide gas and the formation of water.

iii. When dilute hydrochloric acid reacts with copper oxide the following reactions takes place : -

CuO(s) + 2HCl (aq) → 2CuCl₂(s) + H₂O (l)

Hence, when an acid reacts with a metal oxide the corresponding salt is formed along with the formation of water.

This reaction could be seen as similar to the reaction between an acid and a base. So, metallic oxides are treated as basic in nature.