Question

Which of the following is a reasonable ground-state electron configuration?

Answer 1

Following Aufbau rule and Hund principle, the order of filling of the orbitals is this:

$1s^22s^22p^63s^23p^64s^23d^{10}...$

So, the first, second, and fourth option are not correct.

The third option does meet the filling order.

Answer: $1s^22s^22p^63s^23p^64s^23d^1$