Already answered your qstn.
plz check your previous one.
Still Again Reposting to make it easy for U:
First draw its structure and identify the stereocentres.
If it exists and has plane os symetry then it would not called as optical isomer.
And this molecule is symmetrical about the central Carbon atom.
The no. os sterocentres are 2.
Hence for the even no. of stereocentres, No. of optical active isomers = > 2^(n-1) => 2^1 = 2.