What is the electron configuration exception for chromium, and how is it achieved?

Chromium does not promote any electrons, resulting in 4s² 3d⁴.

Chromium promotes an electron from the 3d orbital to the 4s orbital, resulting in 4s² 3d⁴.

Chromium promotes an electron from the 4s orbital to the 3d orbital, resulting in 4s¹ 3d⁵.

Chromium promotes an electron from the 4p orbital to the 3d orbital, resulting in 4s² 3d⁵.