Give reasons to explain why:
$(i)$ Carbon dioxide is called a gas?
$(ii)$ $A$ gas fills a vessel completely?
$(iii)$ Gases are so easily compressible,whereas it is impossible to compress a solid or a liquid.

(D) $(i)$ Carbon dioxide is classified as a gas due to the following reasons:
$(a)$ It lacks both a fixed volume and a fixed shape,as it completely fills the container in which it is stored.
$(b)$ It exerts pressure on the walls of the container due to the high kinetic energy and collisions of its particles.
$(ii)$ In gases,the intermolecular distances are very large,and the intermolecular forces of attraction are extremely weak. Because of this,gas particles are free to move randomly in the entire space available to them. Consequently,a gas fills the vessel completely.
$(iii)$ The intermolecular space is maximum in gases,intermediate in liquids,and minimum in solids. When pressure is applied to a gas,the particles move closer together,significantly reducing the volume,which makes gases highly compressible. In contrast,the particles in solids and liquids are already closely packed,leaving very little space for further compression,making them almost incompressible.