Arrange HCl, HI, HBr, HF in increasing order of acidic strength.

Explanation

Both reducing nature and acidic character depends upon the tendency to lose `H^(+)` ions. `H^(+)` ion from HI can be released more easily than from HF. It can be explained as follows : i) H-bonding : In H-F, H-atom is involved in H-bonding and cannot be. easily donated.
ii) Bond dissociation energy : Bond length of H-1 is more than that of H-F. So HI can easily donate `H^(+)` ion. Therefore, bond dissociation energy of HI is less than that of HF.
Hence, H-I is stronger acid and stronger reducing agent than H-F. The increasing order of acidic and reducing strength of halogen acids is as follows: HF < HCl < HBr < HI