The increasing order of wavelength of absorption for the complex ions(i) $\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$ (ii) $\left[\mathrm{CrCl}_{6}\right]^{3-}$ (iii) $\left[\mathrm{Cr}\left(\mathrm{OH}_{2}\right)_{6}\right]^{3+}$ (iv) $\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]^{3-}$, is