The correct option is
"Cd²⁺".When an element achieves pseudo noble gas configuration
it means it has 18 electrons
in the highest energy level instead of 8.
The electronic configuration of cadmium is:
1s²
2s²
2p⁶
3s²
3p⁶
4s²
3d¹⁰
4p⁶
5s²
4d1¹⁰
and the electron configuration of Cd²⁺ is
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 4d¹⁰
