What is the electron configuration of a ground-state Fe²⁺ ion?
Select one:
a) [Ar] 3d⁶
b) [Ar] 4d⁶
c) [Ar] 4s¹ 3d⁵
d) [Ar] 4s¹ 3d⁵
e) [Ar] 3d⁶