You are given three iron rods. Two of the rods are magnets but the third one is not. How could you use the three rods to definitively identify the unmagnetized rod?

A magnets always have two poles (north and south), the unmagnetized rod can be identified using properties of the poles of a magnet.

Explanation:

The law of magnetism states that like poles repel, while unlike poles attract. The simple experiment here is to use two rods at a time, keeping one of the poles of the first rod constant, while changing the poles of the other rod.

When the two rods are magnets, attraction and repulsion would be observed between the rods. But for the case of unmagnetized rod and one of the magnetised rod, only attraction is observed between the poles.