Hexafluoroferrate (III) ion is an outer orbital complex. The number of unpaired electrons present in Fe is
5
We know that Fe3+ will have an electronic configuration of 3d5. Depending on whether the ligand that attacks this is weak or strong field, it may or may not cause pairing of electrons. That is the key idea that will help us solve this question.
Since F− is a weak field ligand, it will not cause any pairing of electrons.
Due to Hund's rule, each d-orbital of iron will have one electron resulting in 5 unpaired electrons
∴ [FeF6]3− is sp3d2 hybridized since it is already given that this is an outer orbital complex.