The element having electronic configuration $ns^2(n-1)d^{1-10}(n-2)f^{1-14}$ belongs to:

The correct statement is

The common stable oxidation states of $Eu$ and $Gd$ are respectively

Although $(+3)$ oxidation state is the characteristic oxidation state of lanthanoids,cerium shows $(+4)$ oxidation state also. Why?

The chemistry of the actinoid elements is not so smooth as that of the lanthanoids. Justify this statement by giving some examples from the oxidation states of these elements.

Write a note on oxidation states shown by lanthanoids.