[Co(NH₃)₅Br]²⁺
Ligands and charges on them,
5 × NH₃ = 5 × 0 = 0
1 × Br⁻¹ = 1 × -1 = -1
Charge on sphere = +2
So, putting values in equation,
Co + (0)₅ - 1 = +2
Co + 0 - 1 = +2
Co - 1 = +2
Co = +2 + 1
Co = +3
Result:
Oxidation state of Co in [Co(NH₃)₅Br]²⁺ is +3.
