what is the hybridisation of [Co(OX)3]4- ?plz explain it...........?

Oxidation of Cobalt is +3, it has 3 unpaired electrons in 3d7 orbital and a pair of electrons in 4s2 orbital.

Co+3 loses one electron from 3d orbital and one electron from 4s orbital.

When oxalate ions approach cobalt ion pairing of electrons takes place in the 3d orbital.

Thus the resulting hybridized orbital is d2sp3.