The oxidation numbers for all above ionic molecules can be calculated using assigning variable for unknown oxidation state and following the rule that algebraic sum of all oxidation states of a compound is equal to the charge on the compound.

CrO^-₂ → → x= +3

ClO^-₃→ → x= +5

CrO^2-₄→ → x= +6

MnO^-₄→ → x= +7

The ascending order of increasing oxidation state of the given molecules is: CrO^-₂ <ClO^-₃<CrO^2-₄<MnO^-₄

The correct option suggesting that is option (i).

*Caution must be taken in noticing the charge on the molecule and not taking it as zero, along with that the rules of finding oxidation number should not be violated.