Which of the following arrangements represents the increasing oxidation number of the central atom?

1. CrO2-, ClO3-, CrO42-, MnO4-

2. ClO3-, CrO42-, MnO4-, CrO2-

3. CrO2-, ClO3-, MnO4-, CrO42-

4. CrO42-, MnO4-, CrO2-, ClO3-

Hint: The oxidation number of oxygen atom is -2.
Writing the oxidation number (O.N.) of Cr, Cl and Mn on each species in the four set ions, then,
(1) Cr+3O2-, Cl+5O3-, Cr+6O42-, Mn+7O4-
(2) Cl+5O3-, Cr+6O42-, Mn+7O4-, Cr+3O2-
(3) Cr+3O2-, Cl+5O3-, Mn+7O4-, Cr+6O42-
(4) Cr+6O42-, Mn+7O4-, Cr+3O2-, Cl+5O3-
Only in the arrangement (1), the oxidation number of central atom increases from left to right, therefore, option (1) is correct.