The correct option is C 3
Let the O.N. of Co be x
Where O.N. represnts the oxidation number.
here also,
O. N. of NH3 is zero
O. N. of Cl is - 1
O. N. of Br is -1
∴O.N. of (Co)+6×O.N. of (NH3)+2×O.N. of (Cl)+O.N. of (Br)=0
putting the values,
⇒x+6(0)−1×2−1=0
∴x=+3
So, the oxidation number of cobalt in the given complex compount is +3.