Question

You are given two pieces of iron and nothing else; how will you find which one is the magnet and which one is the non-magnet? Which property of the magnet will you use to answer the question?

Answer 1

Let's consider you gave me two magnetic needle, made of iron..

Now we know that, earth has its own magnetic field. Therefore it will deflect the iron, which is magnetic. The magnetic iron will point along south-north direction. If you slightly rotate it, then it will come back to its equilibrium position.

Therefore I will see, which iron needle is coming back to its original position even after giving slight rotation. This is will magnetic

the other one is non-magnetic..

So, basically I will use the concept: same magnetic poles repeal each other.