The acidic character of hypohalous acid depends on the electronegativity of halogen. As the electronegativity value of halogen increases the acidic strength of hypohalous acid increases. Here, Electronegativity of atom X ( Cl,Br or I ) attached to O decreases down the group, polarity of OH bond decreases, acid strength decreases. It means more the electronegativity of the halogen atom, more the tendency to pull electron and weaker the O−H bond and hence proton ((H)+)can easily be removed.