Correct Answer - C
(c) The electronic configuration of divalent cation is :
`V^(2+)(Z=23),[Ar]3d^(3)`
`Cr^(2+)(Z=24),[Ar]3d^(4)`
`Mn^(2+)(Z=25),[Ar]3d^(5)`
`Fe^(2+)(Z=26),[Ar]3d^(6)`
Since the electronic configuration of `Mn^(2+)` is the most symmetrical, it has the highest third ionisation enthalpy.