Matter can be classified into various groups only the basis of its physical characteristics.

Classification on the basis of physical state: – Matter can exist in any of three physical states. These are:

(a) Solid state (b) Liquid state (c) Gaseous state

Water can exist as ice (solid state), liquid water (liquid state), and steam (gaseous state), under different conditions. Were know that ice only heating melts to give liquid water, and liquid water only further heating gives stream. Same is true for most of the materials (though it may not possible all the time under ordinary conditions). Thus, different forms of matter are inter convertible, i.e. the physical state of a given material can be changed by heating or cooling.