The electronic configuration of the last element of the volatile metal group is:

• A
  $[Rn] \ 5f^{14} \ 6d^{10} \ 7s^2$
• B
  $[Xe] \ 4f^{14} \ 5d^{10} \ 6s^2$
• C
  $[Rn] \ 5f^{14} \ 6d^1 \ 7s^2$
• D
  $[Xe] \ 4f^{14} \ 5d^1 \ 6s^2$