Which of the following is the correct order for the wavelength if...

When central metal ion is same (here ${Ni}^{2 +}$ ), the absorption of colour depends on the ligand.

According to spectrochemical series, various ligands are as follows

$I < {Br}^{-} < {Cl}^{-} < {NO}_{3}^{-} < F^{-} < {H}_{2}O$

$< {NH}_{3} < {NO}_{2}^{-} < {CN}^{-} < CO$

Thus, ${H}_{2}O$~is the weakest ligand among these, therefore the absorbed energy will be lowest in
$\left[Ni\left({H}_{2}O\right)6\right]2 +,$ so it will absorb highest wavelength (red light).

$E ∝ \dfrac{1}{λ}$

$∴$~The order of increasing wavelength is

\left[Ni\left({NO}_{2}\right)6\right]4 - < \left[Ni\left({NH}_{3}\right)6\right]2 + < \left[Ni\left({H}_{2}O\right)6\right]2 +$