(a) The main characteristics of states of matter :

(i) Property: Shape and volume

Solid: They have a definite shape as well as definite volume.

Liquid: They have a definite volume but no definite shape.

Gas: They have neither a definite shape nor a definite volume.

(ii) Property: Compressibility

Solid: Solids are completely in compressible.

Liquid:  Liquids are almost in compressible.

Gas: Gases are highly compressible.

(iii) Property: Rigidity/Fluidity

Solid: Solids possess rigidity.

Liquid:  Liquids can flow, therefore they possess fluidity which is lower than that of gases.

Gas: Gases flow more easily than liquids and thus, have the highest fluidity.

(iv) Property: Kinetic energy

Solid: Their particles have minimum kinetic energy.

Liquid:  Their particles have kinetic energy higher than those of solids.

Gas: Their particles have highest kinetic energy.

(v) Property: Density

Solid: They have high density.

Liquid:  Their density is lower than those of solids but much higher than those of gases.

Gas: They generally have very low densities.

(vi) Property: Diffusion

Solid: They normally do not show the property of diffusion although some rare examples of diffusion of one solid into another are known.

Liquid:  They show the property of diffusion. As a result, solids, liquids and gases all can diffuse into liquids.

Gas: They diffuse very rapidly. The rate of diffusion of a gas is, however, inversely proportional to the square root of its density. Thus, lighter gas diffuses more rapidly than the heavier one.

(b) (i) Rigidity : It is the property which helps a substance to retain its shape when force is applied to it. Splids are rigid while gases and liquids are not.

(ii) Compressibility : The property due to which the particles of matter can be compressed or reduced in volume by applying force or pressure. Gases are highly compressible.

(iii) Fluidity: It is the tendency of a substance to flow. Liquids and gases possess fluidity while solids are rigid.

(iv) Filling a gas container : The molecules of a gas move in all directions and due to negligible inter particle force of attraction can fill the container.

(v) Shape: Solids have definite shape whereas liquids take the shape of the container in which they are placed and gases do not have any shape.

(vi) Kinetic energy: It is the energy possessed by the particles due to their motion. The particles of a gas have maximum kinetic energy due to free motion of gas particles in all directions. Solids have minimum kinetic energy due to least movement of particles.

(vii) Density: Density is the mass of a substance per unit volume. Solids have highest density since their molecules are closely packed.