Which among the following is pure matter?
(1) Carbon–dioxide
(2) Brass
(3) Air
(4) Iron
Answer: (1) Carbon dioxide is a pure substance, provided there is nothing else in it. A “pure substance” does not mean an element. Rather, it means that the given substance has definite physical and chemical properties. “Pure substances” can be either “Elements” or “Compounds” because all substances belonging to these categories have definite physical and chemical properties. A mixture does not have definite physical and chemical properties and combines in varying proportions.
