What is meant by a substance?

A substance is a pure form of matter that has a fixed composition and definite properties. It is made up of only one type of particle and cannot be separated into other substances by physical methods.

Substances can be:

• Elements such as iron, oxygen, and gold.

• Compounds such as water (H₂O) and carbon dioxide (CO₂).

For example, pure water is a substance because its composition remains the same throughout. In chemistry, substances are different from mixtures, which contain two or more substances physically combined.