Ground state electron configuration for Cr?

Answer 1

[Ar] 4s1 3d5

The 4s and 3d subsets are very close in energy, so it works out to be better for Cr to have two haf-filled subsets and more unpaired electrons than it would to be 4s2 3d4.

One of the two exceptions to the Aufbau principle among the first 40 or so elements (the other is copper).

Answer 2

1s2 2s2 2p6 3s2 3p6 3d5 4s1