Arrange the following in increasing order of their crystal field splitting energy:
$I. [Co(H_2O)_6]^{3+}$
$II. [Co(NH_3)_6]^{3+}$
$III. [Co(CN)_6]^{3-}$
$IV. [CoF_6]^{3-}$

• A
  $I < II < III < IV$
• B
  $IV < I < II < III$
• C
  $I < III < II < IV$
• D
  $IV < II < I < III$