Define the following with an example for each:

(a) Pure substance

(b) Impure substance

(c) Alloy

(d) Solution

(e) Heterogeneous mixture

(f) Homogeneous mixture

(a) Pure substances are either elements or compounds. They are homogeneous substances that contain the same kind of atoms or molecules and have a definite set of physical and chemical properties.

(b) A substance in which some other substances are also present in smaller or larger amounts is called a mixture or impure substance.

(c) A homogeneous (solid) mixture of two or more metals or a metal and a non-metal is called an alloy.
Example :

1. Brass: Copper + Zinc
2. Bronze: Copper + Tin + Zinc

(d) The homogeneous mixture of water (or any other solvent) and a substance soluble in it (solute) is called a solution.

(e) A mixture in which its constituents are not uniformly distributed throughout its volume and can easily be seen separately is called a heterogeneous mixture.

(f) A mixture in which its constituents are uniformly distributed throughout its volume and cannot be seen separately is called a homogeneous mixture.