A chemical change is when you mix one or more substances to form a new one. A physical change is when you can apply something to a substance but it doesn't change the substance.
Changing the density, color, and mass of an object it doesn't change the type of substance that object is.
Changing the flammability of something changes the type of substance it is. Well, because its irreversable.
The correct answer is [C] Flammability
Best of Luck!
