Final answer:
A pure substance is a form of matter that has a constant composition and properties throughout the sample. When a pure substance is physically mixed with another substance, it forms a mixture. Examples include dissolving salt in water and mixing iron filings with sulfur.
Step-by-step explanation:
A pure substance is a form of matter that has a constant composition and properties throughout the sample. When a pure substance is physically mixed with another substance, it forms a mixture. The change from a pure substance to a mixture is a physical change. For example, when salt dissolves in water, it forms a mixture of salt and water. In this case, salt is the solute and water is the solvent. Another example is when iron filings are mixed with sulfur, forming a mixture of iron and sulfur. Here, the iron and sulfur retain their individual properties but are physically mixed together.