The number of stereo-isomers possible for [Co(OX)₂(Br)(NH₃)]^2– is ___ [OX = oxalate].

Stereo-isomers are isomers having same molecular formula but different spatial arrangement .Stereo-isomers includes geometrical and optical isomerism both.

total number of stereo-isomers= geometrical +$\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$ Optical isomers.

 =2+$\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\left(2\right)$ =3

hence, correct option is:(A)  3