pH, an important water quality parameter, A. is a measure of acidity in water.…

CONCEPT

pH is a logarithmic measure of hydrogen-ion activity in an aqueous solution: pH = −log10(aH+). It describes the acid–base condition of water; lower values indicate greater acidity, while higher values indicate greater basicity.

Because pH is logarithmic, each one-unit change corresponds to a tenfold change in hydrogen-ion activity. Potability, however, is a multi-parameter judgement and cannot be established by pH alone.

APPLICATION

• Statement A is valid: pH is used to express acidity in water.

• Statement B is valid: the same scale expresses basicity when pH is above the neutral point.

• Statement C is invalid: the conventional aqueous scale extends to 14, so pH is not limited to 10; concentrated solutions can even fall outside the usual 0–14 range.

• Statement D is valid in the standard exam sense: pH represents hydrogen-ion activity, commonly described as hydrogen-ion concentration.

• Statement E is invalid: pH 0 indicates a strongly acidic solution, not potable water, and drinking-water safety requires several quality parameters.

CROSS-CHECK

At pH 0, hydrogen-ion activity is approximately 1 (dimensionless), corresponding ideally to a concentration near 1 mol L−1, whereas neutral water is near pH 7 at room temperature. This independently rejects C and E, leaving A, B and D; therefore the result is A, B and D only.