Which has most stable $$ + 2$$  oxidation state :

Solution :
TIPS/Formulae :
(i) Ion having half filled or full filled orbital have extra stability.
(ii) Larger the size of cation more will be its stability $$P{b^{2 + }}\left( {5{d^{10}}6{s^2}} \right),$$    has the most stable $$ + 2$$  oxidation state because here the $$d$$-orbital is completely filled and is more stable than $$F{e^{2 + }}\left( {3{d^6}} \right).$$   Again $$A{g^ + }\left( {4{d^{10}}} \right)$$   is more stable as here again the $$d$$-orbital is completely filled and $$A{g^{2 + }}$$  is not easily obtained. $$P{b^{2 + }}$$  is more stable compared to $$S{n^{2 + }}\left( {4{d^{10}}5{s^2}} \right)$$    because of its large size.