NCERT Solutions for Class 9 Science Chapter 1
Extra Questions for Practice
Class 9 Chemistry Chapter 1 – Matter in Our Surroundings
- Question 1:
Solids are normally not compressible. Why can a sponge be readily pressed?
A sponge made up of rubber has a large number of fine pores in which air remains filled. When the sponge is pressed, the air from the pores escapes and vacant space are left. Therefore, the sponge can be readily pressed on applying pressure.
- Question 2:
Why does a gas fill the vessel completely in which it is kept?
In a gas , the inter-particle space are very large and inner particle forces are quite weak. Therefore, the particle motion is large. As a result, a gas filled the vessel completely.
- Question 3:
Kelvin scale of temperature is regarded as better than the Celsius scale. Give reason.
In the Celsius scale of temperature we often come across a negative sign for the temperature (e.g., -8.5⁰C). Since the sign is always positive in the Kelvin scale, it is regarded as better.
- Question 4:
Why do we sweat on a humid day?
In humid day, the air around us has already high percentage of water vapours. Therefore, the water coming from the skin gets less opportunity to charge into vapours and remains sticking to our body. We therefore, swear more on a humidity day.
- Question 5:
Why do substance undergo change in physical state?
Substance undergo change in physical state because both inter-particle spaces and inter-particle forces can be changed by changing the condition of temperature and pressure.
- Question 6:
When sugar is dissolved in water, there is hardly an increase in volume. Which characteristic of matter is illustrated by this observation?
This is because of the presence of inter particle space or empty spaces. Particles or molecules of water can fill the empty space in the particles or molecules of sugar and vice versa. That is why there is hardly any change in the volume as a result of dissolution of sugar in water.
- Question 7:
What is the name given to the process when the vapours of a liquid get cooled?
The process is known as condensation.
- Question 8:
Define gaseous state of a substance.
A substance is said to be in the gaseous state if under normal pressure, its boiling point is below the room temperature.
- Question 9:
How does pressure help in the liquefication of a gas?
Increase in pressure helps in the liquefication of a gas. The particles or molecules of a gas come closer and closer as the pressure is being increased gradually. They ultimately condense and as a result, the gas liquefies or changes into the liquid state.
- Question 10:
Solids are generally very heavy while gases are light. Explain.
In the solids, the particle are very closely packed. As a result, the number of particles per unit volume is quite large. Therefore, the solids are normally quite heavy. In the gases, the particles are loosely packed. The number of particle per unit volume is completely small. Therefore, gases are light.