(a) The particles of a gas have maximum kinetic energy. They move with high speed in all directions and can exert pressure on the walls of its container.

(b) Gases neither have a definite shape nor a definite volume. They fill up the container completely.

(c) This is due to the intermolecular space in between the constituent particles is maximum in gases, little less in the liquids and the least in solids. On applying pressure, the gaseous particles come together, where as in liquids and solids, the particles are very close and hence cannot be further brought closer. Hence gases are compressible but not liquids and solids.