When two substances combine but no new substances are formed?

When two substances combine but no new substances are formed, they undergo a physical change rather than a chemical change. This can occur through processes like mixing, dissolving, or blending, where the individual properties of each substance remain intact. An example is mixing salt and water; the salt dissolves, but both the salt and water retain their original properties. Such mixtures can usually be separated by physical means, such as evaporation or filtration.