Which one of the following has the correct order of `Delta_(o)` ?

Options

A. `[Co(CN)_(6)]^(3-) gt [Co(H_(2)O)_(6)]^(3+)`
B. `[Co(H_(2)O)_(6)]^(2+) lt [Co(H_(2)O)_(6)]^(3+)`
C. `[Co(H_(2)O)_(6)]^(3+) gt [Rh(H_(2)O)_(6)]^(3+)`
D. `[Co(NH_(3))_(6)]^(3+) lt [CoF_(6)]^(3-)`

Explanation

(A,B)
(A) `Delta _(o)prop` strength of ligand. `CN^(-)` is stronger field ligand than `H_(2)O.So Delta_(o)` of `[Co(CN)_(6)]^(3-) gt [Co(H_(2)O)_(6)]^(2+) [Co(CN_(6))]^(3)`
(B) `Delta_(o)prop` oxidation state of central metal ion. So `Delta_(o)` of `[Co(H_(2)O)_(6)]^(2+) lt [Co(H_(2)O)_(6)]^(3+)`
Note : `Delta_(o)prop` principal quantum number of central atom/ion i.e.n.