The quantitative measure of the acidity or alkalinity of a solution can be expressed in terms of the ________ scale.

Please help me?

The question is probably referring to the units of measurement used for acidity. As a clue, water is a 7 on this scale, and that is considered neutral.

It's a scale ranging from about 1 to 14, which indicates acidic under 7, neutral at 7 (like DrLang said above) and alkalinity over 7.