Assertion: The acidic strength of halogen acids varies in the order HF>HCl>HBr>HI

Reason: The bond dissociation enthalpy of halogen acids decreases in the order HF>HCl>HBr>HI

The bond dissociation enthalpy of halogen acids decreases in the order HF>HCl>HBr>HI . This is due to the formation of strong intermolecular hydrogen bonds. F being most electronegative and small in size forms very strong hydrogen bonds followed by Cl. Br and I does not take part in the formation of intermolecular hydrogen bonding with water and also they have large size. Thus they are less stable.

Acidic nature is determined by the ability to donate H⁺ ion in solution. HI being the least stable due to its large size and its inability to form strong hydrogen bonds lose H⁺ easily as its bond enthalpy is least making it the most acidic followed by HBr, HCl, HF due to their increasing order of stability.