XX' $$ \to $$ Linear (e.g. ClF, BrF)

XX₃' $$ \to $$ T-Shape (e.g. ClF₃, BrF₃)

XX₅' $$ \to $$ Square pyramidal (e.g. BrF₅, IF₅)

XX₇' $$ \to $$ Pentagonal bipyramidal (e.g. IF₇)

The inertness of s-subshell electrons towards bond formation is known as inert pair effect. This effect increases down the group thus, for Sn, +4 oxidation state is more stable, whereas, for Pb, +2 oxidation state is more stable, i.e., Sn²⁺ is reducing while Pb⁴⁺ is oxidising

The acidic character of the oxoacids increases with increase in oxidation number of the halogen atom i.e.,

HClO < HClO₂ < HClO₃ < HClO₄

Since the stability of the anion decreases in the order.

ClO₄^- > ClO₃^- > ClO₂^- > ClO^–

Acid strength also decreases in the same order.

Cu +4HNO₃ (conc.) $$ \to $$ Cu(NO₃)₂ + 2NO₂ + 2H₂O