In the octahedral crystal field,the correct order of splitting for $I^{-}, H_2O, NH_3$ and $CN^{-}$ ligands is:

• A
  $CN^{-} < NH_3 < H_2O < I^{-}$
• B
  $NH_3 < H_2O < I^{-} < CN^{-}$
• C
  $CN^{-} < I^{-} < H_2O < NH_3$
• D
  $I^{-} < H_2O < NH_3 < CN^{-}$