A chemical change forms a new substance with different properties, while a physical change only alters the state or appearance without forming anything new. Burning paper, curdling milk, and rusting iron all create new substances (ash/CO2, curd, iron oxide), making them chemical changes. But melting wax just changes solid wax to liquid wax — no new substance is formed — so it's a physical change. The correct answer is Melting of wax, option (3).