HCI + H2O ⇌ H3O+ + Cl- in this case, in addition to auto ionisation of water, HCI molecule also produces H3O ion by donating a proton to water and hence [H3O]> [OH]. It means that the aqueous HCI solution is acidic. Similarly in basic solution such as aqueous NH3 , [OH-] > [H3O+] and it is basic.
