Following Aufbau rule and Hund principle, the order of filling of the orbitals is this:
[tex]1s^22s^22p^63s^23p^64s^23d^{10}...[/tex]
So, the first, second, and fourth option are not correct.
The third option does meet the filling order.
Answer: [tex]1s^22s^22p^63s^23p^64s^23d^1[/tex]
