Q.Draw the structures of the optical isomers of [CrCl2(ox)2]3-. Write the formula of Ammine bromido chlorido nitrito-N-platinate (II) ion.

Only the cis isomer of [CrCl2(ox)2]3- lacks an internal plane of symmetry, so only the cis form is chiral and shows optical (mirror-image) isomerism; the trans form is achiral. The named-ion formula is built by writing the ligands in the order given by the name.

Optical isomers of $[CrCl_2(ox)_2]^{3-}$:

This is an octahedral complex with 2 monodentate $Cl^-$ ligands and 2 bidentate oxalate ($ox = C_2O_4^{2-}$) ligands, so it can exist as cis and trans geometrical isomers (depending on whether the two $Cl^-$ ligands are adjacent or opposite):

• The trans isomer (the two $Cl^-$ ligands opposite each other, oxalates in the equatorial plane) has an internal mirror plane, so it is superimposable on its mirror image — achiral, optically inactive.
• The cis isomer (the two $Cl^-$ ligands adjacent, cis to each other) has no internal plane of symmetry, so its mirror image is non-superimposable on the original — this gives a pair of optical isomers (enantiomers), conventionally labelled Δ-cis-$[CrCl_2(ox)_2]^{3-}$ and Λ-cis-$[CrCl_2(ox)_2]^{3-}$, related as left- and right-handed "propeller" arrangements of the two chelate rings around the octahedron.

Formula from the name "Ammine bromido chlorido nitrito-N-platinate(II) ion":

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