The correct option is C [Cr(H2O)6]3+<[Cr(NH3)6]3+<[Cr(NO2)6]3−
For the same cation, stronger the ligand, higher the Δ0.
According to spectrochemical series, ligand strength is in order:
H2O<NH3<NO−2
Hence, Δ0 order:
[Cr(H2O)6]3+<[Cr(NH3)6]3+<[Cr(NO2)6]3−