Matter exists in three states:
(i) Solid: A solid has a definite volume but its shape is not definite, it will depend on the shape of the container in which it is contained,e.e., 5ml each of water, petrol, alcohol kept in different types of containers will have different shapes but the volume of each of these liquids remains the same, i.e., 5ml
(ii) Gas: A gas has neither a definite shape nor a definite volume,e.g., hydrogen, air, nitrogen taken in different containers have the shape and volume of the containing vessel.

(i) Liquid diffusing into solid.If we put a drop of ink on the centre of a clean blotting paper, we find the liquid spreads out by diffusing into the blotting paper which is a solid.
(ii) Solid diffusing into liquid.When we put a crystal of potassium permanganate in water, slowly the colour of potassium permanganate spreads throughout water.
(iii) Diffusion of a solid into a solid.Diffusion of solids into solids is very very slow.So diffusion of a solid into other solids is rare and very small.When we write on a blackboard with a chalk, we can easily clean it.But if it is left uncleaned for few days, it becomes difficult to clean the blackboard.This is because there is a slight diffusion of chalk particles.i.e., solid into the solid blackboard.

Light and sound are not considered as matter because they have no mass and do not occupy space.

common properties of liquids and gases:
(a) Both have fluidity.
(b) Both attain the shape of the container.