What is the correct electron configuration of iron (Fe, Z=26)?

A) [Ar] 3d6 4s2

B) [Ar] 3d8

C) [Ar] 4s2 4p6

D) [Ar] 3d5 4s3

Explanation

Iron: [Ar] 3d6 4s2. The 4s orbital fills before 3d, and iron has 8 electrons beyond the Ar core distributed as 3d6 4s2.