Bleaching action of $SO_2$ is due to

Although fluorine is more electronegative than oxygen,the ability of oxygen to stabilize higher oxidation states exceeds that of fluorine. Why?

The element which does not belong to group $15$ is

Assertion : Ozone is an allotrope of oxygen.
Reason : Oxygen is a bluish-coloured liquid and in its singlet state,it is paramagnetic.

Which process is used for the manufacture of $H_2SO_4$?

The quantitative estimation of $O_3$ is based on