Explanation:

Enantiomers are stereoisomers that are non-superimposable mirror images of each other. In order for a pair of compounds to be enantiomers, they must have the same connectivity of atoms but differ in their three-dimensional arrangement.

Let's analyze each option to determine which one will give a pair of enantiomorphs.

a) [Cr(NH3)6][Co(CN)6]
- This compound consists of two different coordination complexes, the hexammine chromium(III) ion [Cr(NH3)6]3+ and the hexacyanocobaltate(III) ion [Co(CN)6]3-. These complexes do not have the same connectivity of atoms, so they cannot be enantiomers.

b) [Co(en)2Cl2]Cl
- This compound contains the coordination complex [Co(en)2Cl2]+, where en is the ethylenediamine ligand. The two en ligands are bonded to the central cobalt atom in a chelating arrangement, forming a five-membered chelate ring. The chlorine atoms are in a cis configuration. If we imagine swapping the positions of the two en ligands, we will obtain the enantiomer of the complex. Therefore, this compound can exist as a pair of enantiomers.

c) [Pt(NH3)4][PtCl6]
- This compound consists of two different coordination complexes, the tetraammine platinum(II) ion [Pt(NH3)4]2+ and the hexachloroplatinate(IV) ion [PtCl6]2-. These complexes do not have the same connectivity of atoms, so they cannot be enantiomers.

d) [Co(NH3)4Cl2]NO2
- This compound contains the coordination complex [Co(NH3)4Cl2]+, where four ammonia ligands and two chloride ligands are bonded to the central cobalt atom. The nitrite ion NO2- is not a ligand in this complex. Therefore, this compound does not have the same connectivity of atoms as the compound in option b, so they cannot be enantiomers.

Conclusion:
The correct answer is option b) [Co(en)2Cl2]Cl, which can exist as a pair of enantiomers by swapping the positions of the two ethylenediamine ligands.