* Equal numbers of H+ and OH- ions define a neutral solution. Pure water, for example, has a balanced concentration of H+ and OH- ions, making it neutral.

* Alkaline solutions have a higher concentration of OH- ions than H+ ions. This imbalance leads to a pH value above 7, indicating alkalinity.

* Acidic solutions have a higher concentration of H+ ions than OH- ions. This imbalance leads to a pH value below 7, indicating acidity.

To summarize:

* Neutral: [H+] = [OH-]

* Alkaline (Basic): [OH-] > [H+]

* Acidic: [H+] > [OH-]