Concept:Sublimation is the direct change of a solid into a gas without first becoming a liquid.Explanation:When heated, NH4Cl, I2 and S8 undergo sublimation.They change directly from the solid state to the gaseous state.However, CaCO3 does not sublime when heated.Instead, CaCO3 decomposes to form calcium oxide and carbon dioxide gas.So CaCO3 is the substance that does not change directly from solid to gas.Answer:C. CaCO3(s)