Account for the following observations
(a) `AlCl_(3)` is a Lewis acid
(b) Though fluorine is more electronegative than chlorine yet `BF_(3)` is a weaker Lewis acid than `BCI_(3)`
(c) `PbO_(2)` is a stronger oxidising agent than `SnO_(2)`
(d) The +1 oxidation state of thallium is more stable than its +3 state.

Explanation

Due to the presence of fully filled less shiling d-and //or f-orbitals in `Pb` and ` Sn` they exhy exhibit inert paire effect and can have tow different oxidation sttes . Whith increase in the number of electron in `d-and //or` f-prbiotals tendency to show inert paire effect inceases and hence in tin `+4` oxidation state will be more stable as compared to lead. Hence `Pb (IV)` compounds will behave as sterong oxidising agnets as comapred to `Sn (IV)` comjpounds . Hence `PbO_2` willl act as stronger oxidaring agent than `SnO_2` .