Which element has the following ground state electron configuration?

Question

Which element has the following ground state electron configuration?

3d 4s

[Ar]

Answer 1

The electron configuration is [Ar] 4s² 3d¹. 4s means we are in period (row) #4 of the periodic table. The 4s subshell gets filled with 2 electrons before the 3d subshell since it is lower in energy. 3d¹ indicates the 1st element in the d-block, which is Sc or Scandium.