Chemistry - Coordination Chemistry Question with Solution | TestHub

The initial complex, ${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_2{\left({\mathrm{H}}_2\mathrm{O}\right)}_2\left({\mathrm{NO}}_2\right)(\mathrm{Br})\right]}^{+}$, has 8 stereoisomers (2 pairs of enantiomers). Replacing ${\mathrm{NO}}_2^{-}$ and ${\mathrm{Br}}^{-}$ with 'en' gives ${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_2{\left({\mathrm{H}}_2\mathrm{O}\right)}_2(\mathrm{en})\right]}^{3+}$, which has 4 stereoisomers (1 pair of enantiomers). The difference is $8-4=4$