NCERT Class 9 Science Chapter 1: "Matter in Our Surroundings" — Intext and Exercise question answers, right?.
Chapter 1: Matter in Our Surroundings
Intext Questions and Answers
Page 3
Q1. Which of the following are matter? Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.
Answer:
Matter has mass and occupies space. So, the following are matter:
- Chair
- Air
- Almonds
- Cold drink
- Smell of perfume (because it consists of particles that spread in the air)
Page 6
Q1. Give reasons for the following observations:
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 not through a solid.
Answer:
a) Gases have particles with high kinetic energy and negligible intermolecular force, so they spread to fill the vessel.
b) Gas particles move randomly at high speed and collide with the walls of the container, exerting pressure.
c) A wooden table has a definite shape and volume, and its particles are tightly packed — typical properties of a solid.
d) Air particles are far apart and easily compressed, while solids have tightly packed particles, making it difficult to pass through.
Page 9
Q1. Convert the following temperature to Celsius scale:
a) 300 K
b) 573 K
Answer:
a) 300 K = 300 – 273 = 27°C
b) 573 K = 573 – 273 = 300°C
Q2. What is the physical state of water at:
a) 250°C
b) 100°C
Answer:
a) At 250°C — Water is in gaseous state (steam).
b) At 100°C — Water is at its boiling point; it exists as both liquid and gas.
Q3. For any substance, why does the temperature remain constant during the change of state?
Answer:
During change of state, energy is used to overcome intermolecular forces, not to increase the temperature.
Q4. Suggest a method to liquefy atmospheric gases.
Answer:
By applying high pressure and lowering the temperature, gases can be liquefied.
Page 10
Q1. Why does a desert cooler cool better on a hot dry day?
Answer:
On a hot dry day, evaporation is faster because the air is dry. Faster evaporation leads to more cooling.
Q2. How does the water kept in an earthen pot (matka) become cool during summer?
Answer:
Water seeps out through pores of the pot and evaporates. Evaporation takes away heat, thus cooling the water.
Q3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer:
Acetone, petrol, or perfume evaporate quickly, absorbing heat from the palm, making it feel cold.
Q4. Why are we able to sip hot tea or milk faster from a saucer than a cup?
Answer:
The surface area is larger in a saucer, leading to faster evaporation and cooling, making it easier to sip.
Q5. What type of clothes should we wear in summer?
Answer:
We should wear light-colored, cotton clothes because they reflect heat and cotton absorbs sweat and helps in its evaporation, cooling the body.
Exercise Questions and Answers (Page 12)
Q1. Convert the following temperatures to the Kelvin scale:
a) 25°C
b) 373°C
Answer:
a) 25°C + 273 = 298 K
b) 373°C + 273 = 646 K
Q2. Give reasons for the following observations:
a) Naphthalene balls disappear with time without leaving any solid.
b) We can get the smell of perfume sitting several meters away.
Answer:
a) Naphthalene balls undergo sublimation, directly changing from solid to gas.
b) Perfume particles diffuse through the air and reach us.
Q3. Arrange the following substances in increasing order of forces of attraction between the particles:
Water, Sugar, Oxygen.
Answer:
Oxygen < Water < Sugar
(Force of attraction: gas < liquid < solid)
Q4. What is the physical state of water at:
a) 25°C
b) 0°C
c) 100°C
Answer:
a) 25°C — Liquid
b) 0°C — Solid and liquid (both) (melting/freezing point)
c) 100°C — Liquid and gas (both) (boiling point)
Q5. Give two reasons to justify:
a) Water at room temperature is a liquid.
b) An iron almirah is a solid at room temperature.
Answer:
a) Water has no fixed shape but fixed volume and flows at room temperature.
b) An iron almirah has a definite shape, volume, and cannot flow — typical of solids.
Q6. Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer:
Ice at 273 K absorbs additional latent heat to melt without any rise in temperature, causing more cooling.
Q7. What produces more severe burns, boiling water or steam?
Answer:
Steam produces more severe burns because it contains extra latent heat of vaporization compared to boiling water.
Q8. Name A, B, C, D, E, and F in the following diagram showing change of its state.
(The diagram shows solid, liquid, gas, and the processes between them.)
Answer:
- A — Fusion (Melting)
- B — Vaporization
- C — Condensation
- D — Solidification (Freezing)
- E — Sublimation
- F — Sublimation
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