(a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following: rigidity. Compressibility. Fluidity. Filling a gas container, shape, kinetic energy and density.

Explanation

(a) The main differences in the characteristics of the three states of matter, solids, liquids and gases are given below :

(b) (i) Rigidity. Rigidity refers to the property of a solid to resist change in its shape (or resist deformation) when an outside force is applied. In most simple terms, rigidity means 'stiffness'. The particles in a solid are very closely packed and there are very strong forces of attraction between them, so solids posses high rigidity. Liquids and gases are not rigid because the positions of their particles are not fixed.
(ii) Compressibility. Compressibility is the property of a fluid (or a solid) due to which its volume decreases when pressure is applied. The particles in gases have large spaces between them due to which their volume decrease too much when pressure is applied on them. So, gases have high compressibility. On the other hand , the particles in solids and liquids are closely packed, so solids and liquids do not have much compressibility.
(iii) Fluidity. The property of flowing easily is called fluidity. Gases and liquids exhibit the property of fluidity, so they are called fluids. Due to large interparticles distance and very weak forces of attraction, gases can flow extremely easily. So, the gases have very high fluidity. And because of comparatively smaller interparticle distances and stronger forces of attraction between their particles, the fluidity of liquids is less than that of gases. Solids are not fluids, they have no fluidity.
(iv) Filling a gas container. A gas fills its container completely because due to high kinetic energy and negligible interparticles forces of attraction, the particles in a gas move with high speeds in all directions and occupy all the space in the container.
(v) Shape. The external form or appearance of a substance is called its shape. A solid has a fixed shape because the particles in a solid are closely packed and their positions are fixed due to strong forces of attraction between them. The liquids and gases do not have fixed shapes because the positions of particles in them are not fixed due to comparatively weaker forces of attraction between them.
(vi) Kinetic energy. The energy possessed by a material due to the motion of its particles is called kinetic energy. At a given temperature, the particles in a gas have the maximum kinetic energy because they move with high speeds due to weakest forces of attraction among them. Liquids have lesser kinetic energy (than gases) whereas solids have the the least kinetic energy at a given temperature.
(vii) Density. The mass per unit volume of a material is called its density. Solids have high densities because their particles are very close together. Liquids have usually lower densities than solids because their particles are somewhat more loosely packed than that in solids. Gases have the lowest densities because their particles are very far apart from one another.