According to the arrhenius model of acids and bases, what happens when an acid is added to water?
the acid increases the concentration of hydroxide ions.
the acid increases the concentration of water molecules.
the acid increases the concentration of salt ions.
the acid increases the concentration of hydrogen ions.

The acid increases the concentration of hydrogen ions.

Explanation:

Arrhenius Base:

According to Arrhenius a base is substance that increase the concentration of hydroxyl ion in aqueous solution. In other words we can say that it increases the OH⁻ when dissociate into water.

Arrhenius acid:

According to Arrhenius an acid is substance that increase the concentration of hydrogen ion in aqueous solution. In other words we can say that it increases the H₃O⁺ when dissociate into water.

The hydrogen ion can not exist in free form so it react with water molecule and form hydronium ion.

HCl + H₂O → H₃O⁺+ Cl⁻

HCl is Arrhenius acid and donate proton.

Water accept that proton.