Classify each change as physical or chemical. a. Sugar burns when heated in a skillet. b. Sugar dissolves in water. c. A platinum ring becomes dull because of continued abrasion. d. A silver surface becomes tarnished after exposure to air for a long period of time.

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1. Identify the type of change: Physical changes involve changes in physical properties without altering the substance's chemical identity, while chemical changes involve a transformation into a different substance.
2. Analyze each scenario: a. Sugar burns when heated in a skillet. This involves a chemical change as sugar reacts with oxygen to form new substances like carbon dioxide and water.
3. b. Sugar dissolves in water. This is a physical change because the sugar molecules are dispersed in water but remain chemically unchanged.
4. c. A platinum ring becomes dull because of continued abrasion. This is a physical change as the dullness is due to physical wear and tear, not a change in chemical composition.
5. d. A silver surface becomes tarnished after exposure to air for a long period of time. This is a chemical change as silver reacts with sulfur compounds in the air to form silver sulfide, a new substance.