The atomic mass of an element M is 39, and the number of neutrons is 20. What would be the electronic configuration of its ion M²⁺?
a) 1s² 2s² 2p⁶ 3s² 3p⁶
b) 1s² 2s² 2p⁶ 3s² 3p⁵
c) 1s² 2s² 2p⁶ 3s² 3p⁴
d) 1s² 2s² 2p⁶ 3s² 3p³