pH of pure water at 25°C, kw = 1 x 10^-14

Explanation

The pH of pure water at 25°C is 7 because water is neutral at this temperature, meaning it has equal concentrations of hydrogen ions (H+) and hydroxide ions (OH-). The ion-product constant for water (Kw) at 25°C is 1 × 10-14, which is the product of the concentrations of H+ and OH-. Mathematically, this means [H+] = [OH-] = 1 × 10-7 M. The pH is calculated as the negative logarithm of the hydrogen ion concentration: pH = -log[H+] = 7. Options A and C are incorrect because they represent extreme acidic and basic conditions, respectively, and Option D is incorrect because one of the listed values (7) is correct.