Which of the following is a physical change?

A physical change is a change in which the chemical composition of a substance remains the same, but there is a change in its physical state or appearance. Out of the options provided, the dissolution of sodium chloride (NaCl) in water is a physical change. This is because the chemical composition of NaCl remains the same before and after the dissolving process. Sodium chloride, which is a solid in its pure form, dissolves in water to form a clear and colorless solution, but the chemical composition of NaCl remains the same. The bubbling of chlorine into water and the passing of steam over heated iron are examples of chemical changes because a new substance is formed with a different chemical composition. The bubbling of chlorine into a jar containing hydrogen is also a chemical change because it results in the formation of hydrogen chloride gas (HCl), which has different chemical properties than the reactants (chlorine and hydrogen). Hence, the correct option is the dissolution of sodium chloride in water.