Concept:A chemical change always produces a new substance, while a physical change does not change the identity of the material.
Explanation:Crumpling of paper changes only its shape and size.
No new substance is formed, so it is a physical change.
Crumpled paper is still paper.
Burning of wood is a combustion reaction that produces ash and gases.
Mixing an acid and a base is neutralisation, which forms salt and water.
Rusting of iron forms rust, a substance entirely different from iron.
Thus, all the other options produce new substances, so they are chemical changes.
The only process that is not a chemical change is crumpling of paper.
Answer:A. crumpling of paper.