(i)-(c),(ii)-(a),(iii)-(e),(iv)-(b)

(i)-(c)- Oxidation state of Manganese in MnO₂ is

x-4=0

x=+4

(ii)-(a) Lower oxidation state of Mn is very stable so +2 is stable

(iii)-(e)In KMnO₄, the oxidation state of Mn is +7

(iv)-(b) Lanthanoid have 5d¹ and 6s² outermost configuration. They can lose these three electrons easily and thereby show an oxidation state of +3