Account for the following observation:
(i) `AlCl_(3)` is Lewis acid
(ii) Though fluorine is more electronegative than chlorine yet `BF_(3)` is a weaker Lewis acid than `BCl_(3)`
(iii) `PbO_(2)` is a stronger oxidising agent thatn `SnO_(2)`
(iv) The +1 oxidation state of thallium is more stable than its +3state.

Explanation

(i) `AlCl_(3)` is a Lewis acid because the central Al atom has a sextel of electrons after sharing. It is electron deficient and `AlCl_(3)` behaves as a Lewis acid.
(ii) For answer, consult section 11.12.
(iii) +2 oxidation state of Pb in `PbO_(2)` is more stable than +2 oxidatin state of Sn in `SnO_(2)` due to greater inert pair effect. This means that `PbO_(2)` is a stronger oxidising agent than `SnO_(2)` and changes to +2oxidision state more easily.
(iv) For answer, consult section 11.2.