The correct option is C +2
Firstly, the overall (addition of all) oxidation state of a neutral compound must be zero. In [Pt(NH3)3Cl]Cl, the central metal atom is the Platinum(Pt).
[Pt(NH3)3Cl]Cl, ionises into [Pt(NH3)3Cl]+ and Cl−
Let us consider the oxidation state of Pt in this compound to be x. We know that ammonia is a neutal ligand and Chlorine is a monodentate ligand which has a unit negative charge.
∴ [x +(3×0)−1] = −1
x = +2