What ion do bases release in water that affects pH?

Bases are substances that, when dissolved in water, increase the concentration of hydroxide ions (OH⁻) in the solution. This release of hydroxide ions is significant because they play a crucial role in determining the pH of the solution. The pH scale measures the acidity or basicity of a solution, with lower pH values indicating higher acidity and higher pH values indicating higher basicity.

When a base dissolves in water, it contributes hydroxide ions, which can react with hydrogen ions (H⁺) present in the solution, effectively reducing the concentration of hydrogen ions. This reaction increases the pH level, making the solution more basic. Therefore, the presence of hydroxide ions is what characterizes the basic properties of a solution and directly influences its pH.

The other ions mentioned—carbonate, nitrate, and phosphate—serve different purposes in various chemical contexts, but they do not have the same direct impact on pH as hydroxide ions do by increasing basicity.