Question

Explain:
(i) Why do transition elements show variable oxidation state?
(ii) Give two differences between Lanthanide and Actinide.

Answer 1

(i) Transition metals show variable valency because the energy subshell $(n-1)d$ and $ns$ are very close. Thus possibility to lose electron from $ns$ subshell as well as from $(n-1)d$ subshell is very much if there are unpaired electrons. So oxidation state of these metals only increase.
(ii)

Lanthanide	Actinide
(1) Lanthanide show oxidation state of $+3$ mainly and $+2$ and $+4$ in few compounds. (2) Tendency to form complex compound is low.	(1) Actinides show $+3$ oxidation state together with $+4$, $+5$ and $+6$ in all compounds. (2) Tendency to form complex compound is more than lanthanides.