To calculate the pH of a 0.1 M solution of hydrochloric acid HCl , we can use the formula:pH = -log10[H+]Hydrochloric acid is a strong acid, which means it dissociates completely in water. Therefore, the concentration of H+ ions in the solution will be equal to the concentration of HCl. In this case, the concentration of H+ ions is 0.1 M.Now, we can plug this value into the formula:pH = -log10 0.1 pH = - -1 pH = 1So, the pH of a 0.1 M solution of hydrochloric acid HCl at 25C is 1.