In `PbO_(2)` and `SnO_(2)`, both lead and tin are present in `+4`-oxidation state. But due to stronger inert pair effect, `Pb^(2+)` ions is more stable than `Sn^(2+)` ions . In other words, `Pb^(4+)` ions i.e. `PbO_(2)`, is more easily reduced to `Pb^(2+)` ions than `Sn^(4+)` ions are reduced to `Sn^(2+)` ions. Thus, `PbO_(2)` acts a stronger oxidising agent than `SnO_(2)`.
