What is the pH formula?
A.\[ - {\log _{\text{e}}}\left[ {{{\text{H}}^ + }} \right]\]
B.\[ - {\log _{10}}\left[ {{{\text{H}}^ - }} \right]\]
C.\[ - {\log _{10}}\left[ {{\text{O}}{{\text{H}}^ - }} \right]\]
D.\[ - {\log _{10}}\left[ {{{\text{H}}^ + }} \right]\]

Hint:The pH of the solution can be defined as the negative logarithm to the base ten of the hydrogen ion concentration in a solution. It is used to classify a solution as acidic, basic or neutral.

Complete answer:
The pH of the solution is used as a measure of the hydrogen ion concentration of the solution. Whenever any substance having a replaceable hydrogen ion is put in water, such the acids and the alcohols to some extent, then due to the difference in the electronegativity, the replaceable hydrogen atom in the acid or alcohol molecule ionize in order to release the proton which takes the electron pair from the water molecules forming co-ordinate covalent bond with the oxygen atom resulting to the hydronium ion. The amount of the hydrogen ions released in the medium is the measure of the pH of the solution. Hence it can be mathematically stated as,
pH = \[ - {\log _{10}}\left[ {{{\text{H}}^ + }} \right]\]

Hence, the correct answer is option D.

Note:
The pH of the solution is an important parameter in determining the course of the reaction. Any slight change in the reaction conditions can highly alter the reaction. The pH of the substance is measured according to the pH scale in which the range of the pH is from 0 to 14, and the value of 0 is for the high strength acids while the pH value of 14 is for the high strength bases. The pH of water is 7 and it is the neutral value in the pH scale.