Class 9 Science

States of Matter

There are three states of matter: solid, liquid and gas.


Matters which have fixed volume and shape are called solids. Examples: stone, wood, brick, ice, sugar, salt, coal, etc. All metals are solid except mercury and gallium.

Properties of solids


Matters which have fixed volume but indefinite shape are called liquids. Examples: milk, water, petrol, kerosene, alcohol, oil, etc. Since liquid can flow, it is also called fluid.

Properties of liquid


Matters which have indefinite shape and volume are called gases. Examples: air, oxygen, hydrogen, nitrogen, carbon-dioxide, etc.

Properties of gas

Cause of different physical states of matters

The physical states of matter depend upon three main factors:


Because of great force of attraction particles of solids are closely packed together. This makes the space between particles of solids almost negligible. The lowest kinetic energy of particles does not allow the movement of particles.

The great force of attraction, the least space between particles of solids and the lowest kinetic energy of particles keep the particles at fixed places. Because of the combination of these characters certain matters exist in the solid state.


Because of more space between particles and more kinetic energy the particles of liquid slide over one another. These characters make certain matters to exist in the liquid state. Liquid can flow because its particles can slide over one another.


The particles of gases are loosely packed, and move at high speed. These characters enable certain matters to exist in the gaseous state.

Other states of matter

Plasma and BEC

Plasma and BEC (Bose-Einstein Condensate) are considered as states of matter other than solid, liquid and gas. These are known as the fourth and the fifth states of matter.


It is considered as the fourth state of matter. Plasma is similar to gas. Particles of plasma are made of free electrons and ions.

Plasma is one of the most commonly occurring states of matter in the universe. Plasma occurs naturally in the stars. All stars are made of plasma. Stars glow because of the presence of plasma. Plasma is formed because of nuclear fusion in stars. Our sun glows because of the presence of plasma.

Plasma TV got its name because of the presence of plasma in it. Plasma is also found in fluorescent light or neon sign. Plasma is formed when electricity is passed through a fluorescent tube or neon sign, which makes them glow.

Bose-Einstein Condensate (BEC)

It may be considered as the fifth state of matter. Satyendra Nath Bose and Albert Einstein predicted about this state of matter, that’s why it got its name as Bose-Einstein Condensate (BEC).

Plasma and BEC are have opposite characters. Plasma is a super hot and super excited atom while Condensate has super cool and super unexcited atoms.

BEC had been obtained by cooling the vapor of rubidium-87 at super low temperature by Eric Cornell and Carl Wieman on June 5 1995. After that, Wolfgang Ketterle also obtained BEC from sodium-23 at MIT, USA. Cornell, Wieman and Ketterle got Nobel Prize in Physics for this achievement in 2001.


See Answer

1: (a) Brick, 2: (b) Oil, 3: (d) Air, 4: (a) Stone, 5: (b) Oil, 6: (c) Air, 7: (d) Salt, 8: (a) Air, 9: (a) Air, 10: (c) Dumbbell