Number of unpaired electrons present in the ground state of Fe3+ are (Atomic number of Fe = 26).

Explanation

Neutral iron is [Ar] 3d6 4s2, and forming Fe3+ removes both 4s electrons and one 3d electron, leaving 3d5. By Hund's rule those five electrons occupy the five d orbitals singly with parallel spins, so all five are unpaired, and that half filled arrangement is what makes Fe3+ so stable. Removing d electrons before the 4s pair is the standard error.