Melting lead is a physical change, burning lead is a chemical change, and generating heat when lead reacts with sodium hydroxide is a physical change.
Physical: Melting lead is a physical change because it involves a change in state from solid to liquid without altering the chemical composition. It is reversible upon cooling.
Chemistry: Burning lead is a chemical change as it involves a reaction with oxygen to form new substances such as lead oxide. This change is irreversible.
Physical: Generating heat when lead reacts with sodium hydroxide to form lead(II) hydroxide is a physical change as it involves a temperature change without altering the lead's chemical identity.
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