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Q.
Ammonia is a Lewis base and it forms complexes with many cations. Which one of the following cations does not form a complex with ammonia?
BHUBHU 2009
Solution:
Ammonia is a Lewis base. It forms complexes with transition elements like $Ag ^{+}, C u^{2+}$ and $C d^{2+}$ while it does not form complex with $P b^{2+}$ because $Pb$ is not a transition element.
$AgCl +2 NH _{4} OH \rightarrow\left[ Ag \left( NH _{3}\right)_{2}\right] Cl +2 H _{2} O $
$CuSO _{4}+4 NH _{4} OH \rightarrow\left[ Cu \left( NH _{3}\right)_{4}\right] SO _{4}+4 H _{2} O$
$CdSO _{4}+4 NH _{4} OH \rightarrow\left[ Cu \left( NH _{3}\right)_{4}\right] SO _{4}+4 H _{2} O$