On the basis of physical classification, matter can be classified mainly into three states.
(i) solid state
The state of matter which has a definite volume and shape is called a solid state. In this state the particles of matter are very close together, that is, the interatomic space between them is very less. Due to which they cannot move independently, so they can vibrate only on their own axis. A well-ordered crystal lattice exists between solids, in which the constituent particles are tightly bound. Due to which solids are hard, and their density is high. Example-wood, rock, ice, brick, etc.
(ii) liquid state
The state of matter which has a definite volume but not shape is called a liquid state. In this state the constituent particles are located at a greater distance than the particles of the solid and the force of attraction between them is less. Due to which the particles of liquid move freely within a certain boundary line. Due to the particles being in a state of regular motion, they assume the shape of the vessel in which they are kept. Since the particles of liquids keep sliding on each other in a haphazard manner, due to this the property of fluidity is found in liquids. Example- water, alcohol, milk, oil, etc.
(iii) gaseous state
The state of matter whose volume and shape are both uncertain is called the gaseous state. In this state the force of attraction between the particles of matter is weak and they are present far and wide, due to which they keep on moving randomly and assume the volume and shape of the vessel in which they are kept. Due to the large distance between the particles, they can be compressed by external pressure. Example- hydrogen, air, oxygen, etc. Difference between Gas and Vapour: The substance which is in gaseous state at ordinary temperature is called gas, whereas the substance which is in any other state at ordinary temperature and gaseous state at higher temperature is called vapor.