The total number of electrons in the ground state of chromium with magnetic quantum number, m = 0 is:
10
12
13
11
Cr has 1s22s22p63s23p63d54s1 configuration in the ground state.
Total electrons with m = 0 are 2 + 2 + 2 + 2 + 2 + 1 + 1 = 12