The $[Fe(CN)_6]^{3-}$ complex ion

Which of the following complexes will be the most stable?

Identify the complex with the maximum conductivity.

The brown ring test for $NO_2^-$ and $NO_3^-$ ions is due to the formation of which of the following complex ions?

The $IR$ stretching frequencies of free $CO$ and $CO$ in $[V(CO)_6]^-$,$[Cr(CO)_6]$ and $[Mn(CO)_6]^+$ are $2143 \, cm^{-1}$,$1860 \, cm^{-1}$,$2000 \, cm^{-1}$ and $2090 \, cm^{-1}$,respectively. Then the correct statement about metal carbonyls is:

During the estimation of nickel,we prepare nickel dimethylglyoxime,a scarlet red solid. This compound is . . . . . . .