Which best describes the ph scale?
acids measure below 7.
bases measure below 7.
acids and bases measure above 7.
bases and acids measure at 7.

The correct answer is Acids measure below 7.

pH ( Potential of hydrogen) is used to measure the basicity ( alkalinity) or acidity of water soluble substances.

The value on pH scales lies from 0 to 14 where 7 indicates a neutral pH that corresponding to neutral solutions like water.

Any value below 7 indicates that the solution is acidic ( like Hydrochloric acid) and above 7 indicates that the solution is alkaline ( base like sodium hydroxide).

Thus, acids measure below 7 is the right answer.