Compounds that formally contain `Pb^(4+)` are easily reduced to `Pb^(+2)` .The stability of the lower oxidation state is due to `"…….."` .

Answer

Inert pair effect

Explanation

Compounds that formally contain `Pb^(4+)` are easily reduced to `Pb^(2+)`. The stability of the lower oxidation state is due to inert pair effect.
In the periodic table, inert pair effect increases down the group. So in group `14`, the stability of smaller oxidation state of `+2` goes on increasing down the group. `Pb^(4+)` has an oxidising nature and `Br^(ɵ)` and `I^(ɵ)` have reducing nature, so `Pb^(4+)` is reduced to `Pb^(2+)`.
`Pb^(4+)+2Br^(ɵ) rarr Pb^(2+)+Br_(2)`
`Pb^(4+)+2I^(ɵ) rarr Pb^(2+)+I_(2)`