Which of the following elements has a completely filled $4f$ orbital in its ground state electronic configuration?

Match the following:

List-$I$ (Element)	List-$II$ (Block)
$(A)$ $Ra$	$(I)$ $p$-block
$(B)$ $Uuq$	$(II)$ $s$-block
$(C)$ $Ds$	$(III)$ $f$-block
$(D)$ $Fm$	$(IV)$ $d$-block

The correct answer is

In the $3d$ series,the metal having the highest $M^{2+}/M$ standard electrode potential is .... .

Which of the following pairs of elements does $NOT$ represent chemical twins?

Assertion : Transition metals show variable valency.
Reason : Transition metals have a large energy difference between the $ns^2$ and $(n-1)d$ electrons.

The electronic configuration of Gadolinium ($Gd$,$Z = 64$) is: