Which of the following compounds is brown coloured?

The colour of $CuCr_2O_7$ solution in water is green because

Among the statements $(a)-(d)$,the incorrect ones are:
$(a)$ Octahedral $Co(III)$ complexes with strong field ligands have very high magnetic moments.
$(b)$ When $\Delta_{0} < P$,the $d-$electron configuration of $Co(III)$ in an octahedral complex is $t_{2g}^{4} e_{g}^{2}$.
$(c)$ Wavelength of light absorbed by $[Co(en)_{3}]^{3+}$ is lower than that of $[CoF_{6}]^{3-}$.
$(d)$ If the $\Delta_{0}$ for an octahedral complex of $Co(III)$ is $18,000 \ cm^{-1}$,the $\Delta_{t}$ for its tetrahedral complex with the same ligand will be $16,000 \ cm^{-1}$.

Select the correct statement$(s)$ regarding the $[Ni(DMG)_2]$ complex compound.

$0.001 \ mol$ of $Co(NH_3)_5(NO_3)(SO_4)$ was passed through a cation exchanger. The acid coming out of it required $20 \ mL$ of $0.1 \ M$ $NaOH$ for neutralization. Hence,the complex is:

$[Ni(CO)_4]$ is diamagnetic. Which of the following statements is correct for this complex?