Question

what is the reason of exceptional configuration of chromium (Cr24)?

Answer 1

Cr has 6 electrons in its 3d shell.These 6 electrons arrange themselves in symmetric manner considering hund's rule .As we know,symmetric is one of the most stable state in chemistry.So Cr has all the 6 electrons arranged in the first 3 subshells of 3d shell.
Hope this helps.
Himanshu.