Why are metals flexible?
-atoms of metals can become smaller.
-light bounces off the moving electrons.
-atoms of metals can roll over each other.
-moving electrons create electricity and transfer heat.

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.

The correct answer is "atomic weight".