Question

How many electrons have magnetic Quantum number equal to zero in the ground state electronic configuration of Fe+3 ion

Answer 1

The magnetic quantum numberdistinguishes the orbitals available within a subshell, and is used to calculate the azimuthal component of the orientation of orbital in space. Electrons in a particular subshell (such as s, p, d, or f) are defined by values of ℓ (0, 1, 2, or 3).
So electrins having magnetic number zero means number of electrons in s subshell.

Atomic num of Fe is 26 and that of Fe 3+ is 23.
[Fe 3+] configration is 1s2 2s2 2p6 3s2 3P6 3d3 4s2.
Therefore total num of electrons in s subshell is 8.