Answer:
Mn(IV): 3 outer-shell d electrons
Co(III): 6 outer-shell d electrons
Fe(II): 6 outer-shell d electrons
Ni(II): 8 outer-shell d electrons
Step-by-step explanation:
Mn(IV):
The ion is Mn⁴⁺, so it has lost 4 valence electrons. The ground state electronic configuration of Mn is [Ar]3d ⁵ 4s ². When the neutral atom loses 4 electrons, the electronic configuration is [Ar]3d ³.
outer-shell d electrons = 3
Co(III):
The ion is Co³⁺, so it has lost 3 valence electrons. The ground state electronic configuration of Co is [Ar]3d ⁷4s ². When the neutral atom loses 3 electrons, the electronic configuration is [Ar]3d ⁶.
outer-shell d electrons = 6
Fe(II):
The ion is Fe²⁺, so it has lost 2 valence electrons. The ground state electronic configuration of Fe is [Ar]3d ⁶4s ². When the neutral atom loses 2 electrons, the electronic configuration is [Ar]3d ⁶.
outer-shell d electrons = 6
Ni(II):
The ion is Ni²⁺, so it has lost 2 valence electrons. The ground state electronic configuration of Ni is [Ar]3d ⁸4s ². When the neutral atom loses 2 electrons, the electronic configuration is [Ar]3d ⁸.
outer-shell d electrons = 8