Answer:
Option B. [Ar] 4s² 3d⁷
Step-by-step explanation:
The condensed form of the electronic configuration of of cobalt, Co can be written by using the closest noble gas element before the cobalt element.
Cobalt has atomic number of 27. The noble gas element before cobalt is argon (Ar).
Thus, we can write the electronic configuration of cobalt, Co as follow
Co (27) => [Ar] 4s²3d⁷