Answer: D. Sugar burns when heated on a skillet.
A chemical reaction is one that when it occurs, new substances are formed, and it is not easily reversible by simple chemical processes.
A. When sugar dissolves in water, no new substances are formed. Rather, the dissolution implies a change of state. The process can be easily reversed by simple evaporation to dryness.
B. When solid CO2 is shattered by a hammer, no new substances are formed. The CO2 retains its crystalline structure.
C. When ice undergoes fusion to form liquid H2O, only a change in state occurs. The process can be easily reversed by freezing the liquid H2O.
D. When sugar burns when heated in a skillet, the chemical bonds change. This is not easily reversible.
E. When butane in a lighter evaporates, what occurs is a change of state. The process can be reversed by a simple condensation process.