Question

Strong heating of ammonium chloride is a physical change.how?

Answer 1

here is your answer:

Test tube of ammonium chloride (NH4Cl) being heated over a bunsen burner flame. Ammonium chloride decomposes readily when heated, but condenses in the cooler area at the top of the test tube. This is a reversible reaction, where the ammonium chloridedecomposes into the gases ammonia (NH3) and hydrogen chloride (HCl).

sublimation refers to a physical change of state and is not used to describe the transformation of a solid to a gas in a chemical reaction. For example, the dissociation on heating of solid ammonium chloride into hydrogen chloride and ammoniais not sublimation but a chemical reaction.

Answer 2

The products ammonia and HCl combine to fork NH4Cl . This also a chemical change.
Similar example is seen in
When a candle burns, both physical and chemical changes occur.
on heating candle wax melts and form liquid. it is a physical change. since again turns into solid wax on cooling. this is a physical change.
when u light candle, the wax present near the wick will melt , wick absorb the liquid wax. the liquid wax vaporize due to heat  and give new substances like Co2 , soot,water vapor . This is a chemical change