States of Matter

The solid states can be defined as a matter with definite shape, distinct boundaries and fixed volume. Their particles are tightly packed and have very strong force of attraction between the particles, due to which they have negligible compressibility. They are rigid as they have tendency to retain their shape when subjected to an external force.

We can have some doubts in our mind like if solids are rigid then why rubber band is stretchable?  

Answer - Due to the elastic property of rubber particles, they are stretchable up to a limit when applied external force and regain its original shape when force is removed.  

Now, If solids have no compressibility why sponge is compressible?

Answer -  Due to the air in the pores of sponge. A sponge has minute holes, in which air is trapped and when we press it, the air is expelled out and we are able to compress it.  

Liquids have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept. Suppose, we have one liter of water in a water bottle. Now, when we transfer the water from bottle to a jug, the volume will remain one liter, but water will take the shape of the jug. 

So, we can say that liquids flow and change shape, so they are not rigid but can be called fluid

Gases have neither fixed shape nor fixed volume. The gaseous particles moves very fast and have almost negligible forces of attraction between the particles. he smell of hot cooked food reaches us in seconds; compare this with the rate of diffusion of solids and liquids. Due to high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.

The gaseous molecules have lot of space between them and are highly compressible as compared to liquids & solids. Oxygen supplied in hospitals as a compressed gas in cylinders.  Due to its high compressibility, large volumes of a gas can be compressed into a small cylinder and transported easily.