Correct Option: D

In chemistry, pH is a measure of the activity of the (solvated) hydrogen ion. P [H], which measures the hydrogen ion concentration is closely related to, and is often written as, pH. Pure water has a pH very close to 7 at 25°C. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. A pH of 7 is treated as neutral.