What is the pH of a neutral solution at 25 degrees Celsius?

• A. 6
• B. 7
• C. 8
• D. 9

Answer: (B)

The pH of a neutral solution at 25 degrees Celsius is 7. This is based on the definition of pH, which is a measure of the hydrogen ion concentration in a solution. In pure water, the concentrations of hydrogen ions (H⁺) and hydroxide ions (OH⁻) are equal, both at 1 x 10⁻⁷ M. Since pH is calculated as the negative logarithm (base 10) of the hydrogen ion concentration, a concentration of 1 x 10⁻⁷ M translates to a pH of 7. This value serves as a reference point in the pH scale, which ranges from 0 to 14, with lower values indicating acidity and higher values indicating alkalinity. Therefore, a pH of 7 indicates a neutral solution, where the solution is neither acidic nor basic.