Question

Give reason;
A) A gas completely fills the container in which it is kept.
B) A gas exerts pressure on the wall of a container.
C) A wooden table is called a solid.
D) We can easily move our hands through air but to do so through a solid block we need a karate expert.

Answer 1

Hint: Matter is composed of the simplest particles called atoms and molecules. Solid, liquid and gases are three states of matter.

Complete answer:
> Anything that has mass and occupies space is called matter. We all have studied Dalton’s law which says that every matter is made up of the simplest particles or the building blocks. These building blocks are known as atoms, molecules or ions.
> In a solid the molecules are very tightly packed. The force of attraction between them is so high that they are held together and can’t move. They could only vibrate. They have definite shape and volume.
> In a liquid the molecules are little loosely packed. The force of attraction between them is lesser. They do not have definite shape but have definite volume.
> In a gaseous state the molecules are very-very loosely packed. The force of attraction between the molecules is very weak. So, the molecules cannot stay held together and the gaseous particles keep on moving in different directions. They do not have definite shape or volume.
Now let us answer the given questions.
A) A gas totally fills the container where it is kept because it does not have definite volume. Its molecules are very-very loosely packed. The force of attraction between them is very weak. So, the molecules cannot stay held together and keep on moving in different directions.
B) A gas exerts pressure on the wall of a container because in gaseous matter the molecules are loosely packed. The force of attraction between the molecules is very weak. The molecules keep on moving in different directions and collide with the wall of the container. Due to the collision they exert pressure.
C) A wooden table is called a solid because its molecules are very tightly packed. It has a fixed shape and fixed volume. It is hard.
D) We can easily move our hands through air but to do so through a solid block we need a karate expert. This is because air is a gaseous substance. Its particles are apart and moving in different directions. So, our hand can cut through the gap. On the other hand, solid molecules are very tightly packed. The force of attraction between them is so high that they are held together and can’t move. They could only vibrate. If we try to cut through it, we would get badly hurt by the open upper surface of the closely and tightly packed molecules. So, only a karate expert can do so.

Note: To solve these kinds of questions, you have to remember the particle nature of matter. Also recollect how the particles/molecules are packed in various states of matter. In gases molecules are moving in different directions. In liquid the particles move slowly whereas in solid the particles are very tightly packed.