Question

Which of the following orders is incorrect regarding oxyacids of chlorine and the hydrogen halides?

• A. Thermal stability: $HClO<HCl{O}_2<HCl{O}_3<HCl{O}_4$
• B. Acidic strength: $HClO<HCl{O}_2<HCl{O}_3<HCl{O}_4$
• C. Oxidising power: $HClO<HCl{O}_2<HCl{O}_3<HCl{O}_4$
• D. Reducing power: $HF<HCl<HBr<HI$

Answer 1

The correct option is C Oxidising power: $HClO<HCl{O}_2<HCl{O}_3<HCl{O}_4$

The thermal stability of oxoacids increases with increase in oxidation number of chlorine atom.

As the the number of bonded oxygen atom increases, the more electrons will be pulled away from the $O-H$ bond, which will make the $O-H$ bond weaker further. Thus $HCl{O}_4$ is the strongest acid.

The oxidation state of chlorine in $HClO,HCl{O}_2,HCl{O}_3,HCl{O}_4$ is $+1,+3,+5$ and $+7$ respectively.
Since, the oxidation state of $Cl$ in $HCl{O}_4$ is the highest, it should have the highest oxidising power. But here, stability plays an important role. Lower the stability, more is the oxidising power.

In case of hydrogen halides reducing power increases down the group.