# Give reasons: (a) A gas fills completely the vessel in which it is kept. (b) A gas exerts pressure on the walls of the container. (c) A wooden table should be called a solid (d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.

## (a) A gas fills completely the vessel in which it is kept.

A gas completely fills the vessel in which it is kept.

Reason:

Gases have a negligible intermolecular force of attraction between the particles of gas. The random motion of particlesย  in all the directions is experience in the vessel. Hence, theย gas fills completely the vessel in which it is kept.

## (b) A gas exerts pressure on the walls of the container.

A gas exerts pressure on the walls of the container.

Reason:

They have high kinetic energy and negligible force of attraction so it can move constantly moving with high speed in all directions. Due to this intense random motion of particles, the particles hit each other and also hit the walls of the container with a force. These collisions of the gas particles with the walls of the container exert pressure on the walls of the container.

## (c) A wooden table should be called a solid

A wooden table should be called a solid

Reason:

• It has a definite shape and volume.
• It is very rigid and cannot be compressed i.e., it has the characteristics of a solid.
• There is a strong force of attraction between molecules of wood and intermolecular space is the least.
• The table does not flow when placed.

As the wooden table acquires all the characteristics of a solid (that is fixed shape, volume, rigidity, strong force of attraction, least intermolecular space) hence the wooden table should be called solid.

## (d) We can easily move our hand in the air but to do the same through a solid block of wood we need a karate expert.

We can easily move our hand in the air but to do the same through a solid block of wood we need a karate expert.

Reason:

• Molecules in gases are loosely packed as compared to solid molecules which are densely packed. So we can easily break the force of attraction when we move our hand through the air but it is difficult to break through a solid due to the greater forces of attraction between molecules.
• The particles of the air have large intermolecular spaces and least force of attraction between them. The particles of solid have a minimum amount of intermolecular space and maximum force of attraction between them. Thus, a greater amount of force is required to move the particles of solid apart. Thus, a much greater force is required to move hand through a solid block of wood.

So we need a karate expert to break the solid block of wood.

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