The blank is a measure of how acidic or basic a solution is.

pH of the solution determines the acidity or basicity.

Explanation:

pH of the solution is the negative logarithm of the hydrogen ion concentration of the solution. It is basically the measure of hydrogen ion in a solution.

pH of the solution lies in the range of 1 to 14.

When the pH of the solution ranges from 1 to 6.9, the solution is said to be acidic.

When the pH of the solution ranges from 7.1 to 14, the solution is said to be basic.

When the pH of the solution is 7, the solution is said to be neutral.

Thus, pH of the solution only determines its acidity or basicity.