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

• A

  $\left[\mathrm{Xe}\right]4{\mathrm{f}}^{9}5{\mathrm{s}}^1$

• B

  $\left[\mathrm{Xe}\right]4{\mathrm{f}}^{7}5{\mathrm{d}}^{1}6{\mathrm{s}}^2$

• C

  $\left[\mathrm{Xe}\right]4{\mathrm{f}}^{6}5{\mathrm{d}}^{2}6{\mathrm{s}}^2$

• D

  $\left[\mathrm{Xe}\right]4{\mathrm{f}}^{8}6{\mathrm{d}}^2$