To calculate the pH of a 0.1 M solution of hydrochloric acid HCl , we need to find the concentration of hydrogen ions H+ in the solution. Since HCl is a strong acid, it will completely dissociate in water, meaning that the concentration of H+ ions will be equal to the concentration of HCl.HCl H+ + Cl-[H+] = 0.1 MNow, we can use the pH formula:pH = -log10 [H+] pH = -log10 0.1 pH = 1Since the pH of the solution is 1, which is less than 7, the solution is acidic.