Which statement about pH is correct?

Which statement about pH is correct?

• A. A higher pH indicates higher acidity.
• B. The pH scale is defined only for solutions with water.
• C. A lower pH indicates higher acidity.
• D. Neutral solutions have a pH of 5.

Answer: (C)

The main idea here is how pH relates to acidity. pH is a measure of hydrogen ion activity in an aqueous solution, given by pH = -log10[H+]. Because this relationship is negative, when the hydrogen ion concentration is higher, the pH value becomes lower. So a solution with more H+ is more acidic and has a smaller pH. That makes the statement "a lower pH indicates higher acidity" the correct one. A higher pH does not indicate more acidity; it means less acidity and, above 7, basicity. Neutral solutions are around pH 7 at room temperature, not 5, so the claim about neutral solutions having pH 5 is false. The pH scale is defined for aqueous (water-based) solutions; while related ideas exist for other solvents, the standard interpretation centers on water, so the claim about definition “only for water” is not the standard way to state it, and the direct correct interpretation is about acidity corresponding to lower pH.

The main idea here is how pH relates to acidity. pH is a measure of hydrogen ion activity in an aqueous solution, given by pH = -log10[H+]. Because this relationship is negative, when the hydrogen ion concentration is higher, the pH value becomes lower. So a solution with more H+ is more acidic and has a smaller pH. That makes the statement "a lower pH indicates higher acidity" the correct one.

A higher pH does not indicate more acidity; it means less acidity and, above 7, basicity. Neutral solutions are around pH 7 at room temperature, not 5, so the claim about neutral solutions having pH 5 is false. The pH scale is defined for aqueous (water-based) solutions; while related ideas exist for other solvents, the standard interpretation centers on water, so the claim about definition “only for water” is not the standard way to state it, and the direct correct interpretation is about acidity corresponding to lower pH.