There will be 4 optical isomers of this compound:-

There will be two chiral centres which seem to give 2 × 2 × 2 combinations. However, only 4 isomers are possible.

The (2R, 4R) and (2S, 4S) forms are enantiomers of each other.(2R,4R)-pentane-2,3,4-triol (2S,4S)-pentane-2,3,4-triol

There are also two meso forms:

(2R,3s,4S)-pentane-2,3,4-triol

(2R,3r,4S)-pentane-2,3,4-triol