Which compound is an Arrhenius acid?

(1) CaO (3) K2O

(2) HCl (4) NH3

Arrhenius acid is a substance that when added to water increases the concentration of H1 + ions present. The chemical formulas of Arrhenius acids are written with the acidic hydrogens first.

In the following choices of compounds, HCl or hydrogen chloride or hydrochloric acid is an example of Arrhenius acid.

In other choices, CaO or calcium oxide and K2O or potassium oxide are examples of ionic compound while NH3 or ammonia is an example of covalent compound.