Question

Explain why repulsion is the surest test to confirm whether a material is a magnet?

Answer 1

Not all magnetic materials have north and south poles. Only magnets have poles.
If any material repels, that means the material has both the poles already. It means it is a magnet.
Attraction does not ensure whether the material is a magnet or not because any magnetic material without magnetic poles, may get attracted towards the magnet.