Concept:A physical change only alters the state or form of a substance, without changing its chemical identity.
Explanation:When water boils, it changes from liquid to gas, but the molecules remain
H2O.
No new substance is formed, and the process can be reversed by cooling the steam.
Exposing sodium metal to air causes oxidation, forming new products such as sodium oxide — a chemical change.
Dissolving calcium metal in water produces calcium hydroxide and hydrogen gas, so new substances are formed — a chemical change.
Burning kerosene is combustion, which produces carbon dioxide, water, and other products that cannot be easily recovered — a chemical change.
Therefore, only boiling water is a physical change among the options.
Answer:B: boiling of water.