Chemistry - Coordination Chemistry Question with Solution | TestHub

In $[Co(en{)}_{2}C{l}_2{]}^{+}$, Co is in the +3 oxidation state ($d^6$).

The cis isomer is optically active (shows $\Delta$ and $\Lambda$ forms), whereas the trans isomer has a plane of symmetry, so it is optically inactive. Hence (B) is correct.

Replacing one $C{l}^{-}$ by $B{r}^{-}$ does not change the number of stereoisomers, so (A) is incorrect.

$C{o}^{3+}$ with en (strong-field ligand) forms a low-spin $d^6$ complex ($t_{2g}^6{e}_g^0$), so it is diamagnetic. Hence (D) is correct.

The complex has 18 valence electrons (6 from $C{o}^{3+}$ + 12 from ligands), not 17, so (C) is incorrect.

Correct Answer: B and D