What is the electron configuration of Na+? (Select all that apply)

a) 1s² 2s² 2p⁶
b) 1s² 2s² 2p⁶ 3s¹
c) 1s² 2s² 2p⁶ 3s²
d) 1s² 2s² 2p⁶ 3s² 3p¹