Question

What's oxidising and reducing agent ?

Answer 1

Oxidising agents are those substance which helps to oxidise the another reactant (oxidation reaction) by getting reduced itself on gaining electrons.
Whereas,
Reducing agents are those substance which helps to reduce the another reactant (reduction reaction) by getting oxidize itself on loosing electrons.

Answer 2

The permanganate ion removes electrons from oxalic acid molecules and thereby oxidizes the oxalic acid. Thus, the MnO4- ion acts as an oxidizing agent in this reaction. Oxalic acid, on the other hand, is a reducing agent in this reaction. By giving up electrons, it reduces the MnO4- ion to Mn2+.