The matter is anything that has mass and takes up space and offers resistance to any kind of stress applied to it. Examples are Solid, Liquid, Gas, Plasma and Bose-Einstein Condensate.

An atom is the smallest particle of an element that has all the properties of the element. Note: The particles within an atom are called subatomic particles. Within the nucleus, there are two different kinds of subatomic particles - neutrons and protons - bound close together. A third kind of subatomic particle, called the electron, moves around the nucleus. Protons carry a positive charge, whereas electrons carry a negative charge. Neutrons have no charge.

Gas is a state of matter which has no fixed shape and no fixed volume. It expands freely to fill the whole of a container. In gases, the molecules are very loosely packed. Hence, there is more space between the molecules.