To calculate the pH of a 0.1 M solution of hydrochloric acid HCl , we need to know the concentration of hydrogen ions H+ in the solution. Since HCl is a strong acid, it completely dissociates in water, meaning that the concentration of H+ ions will be equal to the concentration of HCl.In this case, the concentration of H+ ions is 0.1 M. The pH is calculated using the formula:pH = -log10[H+]where [H+] is the concentration of hydrogen ions in moles per liter M .For the given solution:pH = -log10 0.1 pH = - -1 pH = 1So, the pH of a 0.1 M solution of hydrochloric acid HCl is 1.