The pair of the compounds in which both the metals are in the highest possible oxidation state is

Explanation

The highest O.S. of an elements is equal to the number of its valence electrons
(i)`[Fe(CN)(6)]^(3-)`, O.N. of Fe=+3
`[CO(CN)(6)]^(3-)`, O.N. of CO=+3
(ii)`Ce_(2)O_(2)Cl_(2)` of Cr=+6 (Highest O.S. of Cr)
`[MnO_(4)]^(-)` O.N.of Mn=+7 (Highest O.S. of Mn)
(iii)`TiO_(3)`, O.N. of Ti=+6,
`MnO_(2)`O.N. of Mn=+4
(iv)`[CO(CN)(6)]^(3-)`, O.N. of CO=+3,
`MnO(3)`, O.N. of Mn=+6