The correct option is D −log[H+]
pH is a measure of the amount of activity of hydrogen ions (H+) in a solution and thus its acidic or basic nature can be determined. pH is described as “the negative of the logarithm of the molar hydronium-ion concentration". It has no unit but ranges from values 0-14.
pH = -log[H+] or−log[H3O+]
For example, if the concentration of hydronium ions in a solution is 4.0×10−8M, we can use the formula:
pH = −log[4.0×10−8]
pH = 7.40