The $d$-block elements consist mostly of

Statement-$I$: Mercury is liquid at room temperature.
Statement-$II$: In mercury,there is no unpaired $d$-electron and thus,metallic bonding is weakest.

Pairs of elements with the same number of electrons in their respective $4f$ orbital are [Atomic number: $Eu-63, Gd-64, Dy-66, Ho-67, Tm-69, Yb-70, Lu-71, Hf-72$]. Choose the correct answer from the options given below:

Identify the element for which the electronic configuration in the $+3$ oxidation state is $[Ar] 3d^5$:

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

Gadolinium (atomic number $= 64$) is a member of the $4f$ series. Its electronic configuration in the $+3$ oxidation state is $[Xe] 4f^7$. What is the ground state electronic configuration of gadolinium?