Dissolving a solid in water is a physical change.
When a solid dissolves, its particles separate and disperse throughout the liquid, but they do not change their chemical structure. For example, when salt (sodium chloride) dissolves in water, the individual sodium and chloride ions are separated but still retain their identity as sodium and chloride. There is no new substance formed during this process; therefore, it is classified as a physical change.
In contrast, a chemical change involves a transformation that results in the formation of new substances and alters the chemical composition of the original material. Since dissolving merely involves mixing without changing the chemical identity, it remains a physical change.