Complexes $\left[\mathrm{CoX}_6\right]^{3-},\left[\mathrm{CoY}_6\right]^{3+}$ and $\left[\mathrm{CoZ}_6\right]^{3-}$ absorb at 700,475 and 310 nm , respectively. The ligands $\mathrm{X}, \mathrm{Y}$ and Z most likely are, respectively,

• Correct answer
  A

  $\mathrm{F}^{-}, \mathrm{NH}_3, \mathrm{CN}^{-}$
• B

  $\mathrm{CN}^{-}, \mathrm{H}_2 \mathrm{O}, \mathrm{Cl}^{-}$
• C

  $\mathrm{Br}^{-}, \mathrm{NH}_3, \mathrm{NCS}^{-}$
• D

  $\mathrm{I}^{-}, \mathrm{H}_2 \mathrm{O}, \mathrm{OH}^{-}$

Hence, the correct answer is option: 'A'.