Explain that magnetization of an iron nail is a physical change?
It is a rearrangement of the atoms already present, without changing their form chemically.
A chemical change is the result of a change in the atomic structure of an atom - a gain or loss of electrons.
Magnetization simply aligns the existing iron atoms in a certain way due the effect of a magnetic field on their dipole characteristics. It does not change the chemical composition or structure of the iron atoms in any way.