I⁻ acts a strong base.
Explanation:
HI + H₂O → H₃O⁺ + I⁻
HI acts as a strong acid, by means of donating a proton to the water there by forming hydronium ion (H₃O⁺), formed by the addition of H⁺ with H₂O.I⁻ accepts H⁺ ion, there by forming HI in the reverse reaction, so it is a strong base. Any substance which accepts H⁺ ion acts as a strong base.So in the above equation I⁻ is a strong base.