The relative acidic strength, stability and oxidising agent of oxy-acids of chlorine are

In oxyacids of the same halogen in different oxidation states, the acidic nature and thermal stability increase while oxidising nature decreases with increase of oxidation state of halogen. So the correct order of acidic strength will be
$\mathrm{H}\stackrel{+7}{\mathrm{Cl}}{\mathrm{O}}_4>\mathrm{H}\stackrel{+5}{\mathrm{Cl}}{\mathrm{O}}_3>\mathrm{H}\stackrel{+3}{\mathrm{Cl}}{\mathrm{O}}_2>\mathrm{HO}\stackrel{+1}{\mathrm{Cl}}$