The difference between a physical reaction and a chemical reaction is :
A. Composition
B. Size
C. Shape
D. All of above

Hint: We should be having a clear idea regarding the differences between physical and chemical changes. Once we know, we can compare the options.

Complete step-by-step answer:
The difference between a physical reaction and a chemical reaction is composition.




Thus, we can say that the difference between a chemical reaction and a physical reaction is composition. So the correct answer is Option A.

Note: We should have an idea about the physical changes that are limited up to. So apart from the composition here are some other changes which include the physical changes like the texture, colour, temperature, shape, change of state.
Some examples of physical properties of a substance are luster, malleability, ability to be drawn into a thin wire, density, viscosity, solubility, mass and volume.
Some of the indicators of chemical changes are noticeable odour, formation of a precipitate, formation of bubbles and there are many more as well.
Melting and burning of candle wax is an example of both physical and chemical changes. Burning of wood is also an example of both physical and chemical changes. When it is burnt the moisture present in it turns to vapour which is a physical change, while it burns and generates carbon dioxide which is a chemical change.