CBSE Class 11-science Answered

You can not compare perchloric acid and HCl because both are of a different level.

With an increase in oxidation number of a particular halogen atom, the acidic character of corresponding oxoacid increases.

According to Lowry-Bronsted concept, a strong acid has a weak conjugate base and a weak acid has a strong conjugate base. Now, let us consider the stabilities of the conjugate bases ClO₄^-, ClO₃^-, ClO₂^- bases, ClO^- formed from these acids, HClO, HClO₂, HClO₃ and HClO₄ respectively. These anions are stabilised to a greater extent, it has a lesser attraction for proton and therefore, will behave as a weaker base. Consequently, the corresponding acid will be strongest because the weak conjugate base has strong acid and a strong conjugate base has a weak acid and vice versa.

Now the charge stabilization will be minimum. The charge stabilization increases in the order:  ClO^- < -ClO₂^- < -ClO₃^- < -ClO₄^-. This means that ClO^- will have minimum stability and therefore, will have the maximum attraction for H+. Thus,  ClO^- will be the strongest base and so its conjugate acid HClO will be the weakest acid. Similarly, in this series ClO₄^- is the weakest base (maximum stabilized) and its conjugate acid HClO₄ is the strongest acid. Hence, the acidic strength increases in the order: HClO < HClO₂ < HClO₃ < HClO₄.