The first one is the correct choice. We have that bases have [H+] lower than that of water since the product of H+ and OH- concentration in water is constant; in acids H+ are more than OH-, in bases H+ are less than OH- and in neutral PH (water) H+=OH- ; hence in bases OH->H+ . We have that strong bases and strong acids dissociate completely in water (by definition), their pHs are as much far from the middle of the pH scale (7) as possible (around 0 for acids or 14 for bases) and they corrode metals due to how drastic they are.
