If the [H+] of a solution is 0.001 mol/L what is the pH?

A. 12

B. - 2

C. 1

D. 2

pH = 3 (though the option is missing)

Explanation:

We have a solution with a concentration of the hydrogen ion, [H⁺] = 0.001 mol/L = 0.001 M. We can calculate the pH using its definition.

pH = - log [H⁺]

pH = - log 0.001

pH = 3

Since the pH < 7, the solution is acid. Other way to recognize that a solution is acid is when [H⁺] > 10⁻⁷ M at 25°C.