The oxidation number of Pt in [Pt(C2H4)Cl3] is

Dear student,

The compound exists as  [Pt(C2H4)Cl3]^-
If that is the case then 
X + 0+ 3(-1) = -1 
X = +2
According to you : [Pt(C2H4)Cl3] 
X + 0+ 3(-1) = 0
x= +3


Regards