Question

 What effect does the concentration of H⁺ (aq) ions have on the nature of the solution?

Answer 1

If the concentration of H⁺ (aq) ions is increased (>10-7) then the solution become acidic and if the concentration of H⁺ (aq) ions is decreased (<10-7) then the solution become basic in nature.

Answer 2

When acids are added to water, they produce hydrogen ions in water therefore the concentration of the hydrogen ions will increase in water. Since the solution will have more hydrogen ions, it will definitely be acidic in nature.