Gadolinium belongs to the $4\text{f}$ series. Its atomic number is $64$. Which of the following is the correct electronic configuration of gadolinium? 

The electronic configuration is defined as the distribution of electrons of an atom in the atomic or molecular orbitals and is written using the labels for the subshell.

The order in which electrons are filled in atomic orbitals as: 

The number of electrons in each of an atom's orbitals and the total number of electrons in the atom are both determined by the electronic configuration. Gadolinium has an atomic number of 64. Thus, the electronic configuration of Gadolinium is  $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^{10}4{\mathrm{p}}^{6}5{\mathrm{s}}^{2}4{\mathrm{d}}^{10}5{\mathrm{p}}^{6}4{\mathrm{f}}^{7}5{\mathrm{d}}^{1}6{\mathrm{s}}^2$or It can also be represented as $\left[\text{Xe}\right]]4{\text{f}}^{7}5{\text{d}}^{1}6{\text{s}}^2$.

[Xe] represents the electronic configuration of the nearest noble gas

Hence, the correct option is (A).