Arrange the following in the order of property indicated for each set: `HF, HC1, HBr, HI` - increasing acid strength.

Explanation

The relative acid strength of HF, HCI, HBr and HI depends upon their bond dissociation enthalpies. Since the bond dissociation enthalpy of H-X bond decreases from H-F to H-I as the size of halogen atom increases from F to I. Therefore, the acid strength increases in the opposite order, i.e., the acid strength increases in the order:
`HF lt HCl lt HBr lt HI`.