Question

rusting of iron is a chemical change but magnetization of iron is a physical change why​

Answer 1

Rusting of iron is a chemical change cause the rusted iron cannot be again reversed to it's fresh form but magnetisation of an iron bar is a physical change cause after some time it will again come back to it's original form.

Here no new substance is form.

Answer 2

Answer: Iron rust has a different composition from iron and has new chemical properties,  which cannot be reversed.

Magnetization of iron is a temporary change, which does not  change the composition of iron but only physical properties.  

Explanation: Magnetization of iron occurs to due to the temporary alignment of the electrons present in it in one direction only. This is done by rubbing the north pole of the magnet on the middle of the magnet towards its end. It is temporary because after some time, the electrons divert from the alignment.

However, iron rusts because its surface adsorbs oxygen (meaning only the surface reacts with oxygen). It is a chemical reaction where new compounds are formed. So obviously, rusting of iron is a chemical change, but magnetization of iron is not.