Question

Acidity of oxoacids decreases in the order

• A. $HCl{O}_3$ > $HCl{O}_4$ > $HCl{O}_2$ > $HClO$
• B. $HCl{O}_4$ > $HCl{O}_2$ > $HCl{O}_3$ > $HClO$
• C. $HCl{O}_4$ > $HCl{O}_3$ > $HClO$ > $HCl{O}_2$
• D. $HCl{O}_4$ > $HCl{O}_3$ > $HCl{O}_2$ > $HClO$

Answer 1

The correct option is D $HCl{O}_4$ > $HCl{O}_3$ > $HCl{O}_2$ > $HClO$

$HCl{O}_3$ > $HCl{O}_4$ > $HCl{O}_2$ > $HClO$ (Oxidation states: +7 > +5 > +3 > +1)
As the oxidation state of chlorine decreases the acidity of oxoacids decreases. Do note that unlike in the case of Sulphuric and Phosphoric acids series, we have only one proton here.

With more number of electronegative Oxygen atoms attached to the central Chlorine atom, there is a better possibility of charge dispersal in the oxo anion. With greater charge dispersal, the oxoanion becomes more stable and thus the corresponding oxoacid is more acidic!