Which one will have the highest 2nd ionisation energy?

Q. Which one will have the highest 2nd ionisation energy?

A.            1s2 2s2 2p6 3s1

B.            1s2 2s2 2p4

C.            1s2 2s2 2p6

D.            1s2 2s2 2p6 3s2

Answer: 1s2 2s2 2p6 3s1