Question

which refers to a measure of how acidic or basic a solution is?
ph
solubility
reactiveness
hardness

Explanation:

pH is a measure of the hydrogen - ion concentration in a solution, indicating its acidity or basicity. Solubility refers to the ability of a substance to dissolve, reactivity is about how readily a substance undergoes chemical reactions, and hardness is a measure of a material's resistance to deformation.

Answer:

pH