Hots Questions: Matter in Our Surroundings | Science Class 9 PDF Download

Q1: Condensation process is – 
(a) Change of state from gas to liquid
(b) Change of state from liquid to gas
(c) Change of state from gas to solid
(d) Change of state from solid to liquid
Ans: (a)

​The process of changing from gaseous state to liquid state on cooling is called condensation. On cooling the kinetic energy of particles decreases and intermolecular forces of attraction increases therefore gas converted into liquid.

Q2: The temperature at which a liquid starts boiling at atmospheric pressure is known as – 
(a) Melting point
(b) Boiling point
(c) Latent heat
(d) Condensation
Ans: (b)

​When a liquid is heated, it eventually reaches a temperature at which the vapour pressure is large enough that bubbles form inside the body of the liquid. This temperature is called the boiling point.

Q3: On increasing the temperature of the liquid the rate of evaporation is – 
(a) Increase 
(b) Decreases 
(c) No change 
(d) None of these
 Ans: (a) 

The higher the temperature of liquid, the faster the rate of evaporation. This is due to the fact that as the liquid's temperature increases, the molecules of the liquid move about faster, thus increasing the rate of evaporation.

Q4: The physical state of matter which can be easily compressed – 
(a) Liquid
(b) Gas
(c) Solid
(d) None of these
Ans: (b)

In gases, the atoms are much more spread out than in solids or liquids, and the atoms collide randomly with one another. A gas will fill any container, but if the container is not sealed, the gas will escape. Gas can be compressed much more easily than a liquid or solid.

Q5: Name the process by which a drop of ink spreads in a beaker of water – 
(a) Diffusion
(b) Vaporisation
(c) Condensation
(d) Sublimation
Ans: (a)

A drop of ink spreads in a beaker of water through diffusion. This is because the particles in liquids can move around each other, which means that eventually they are evenly mixed. Diffusion is the process of a substance moving from a region of high concentration to a region of low concentration until it is evenly distributed.

Q6: Dry ice is – 
(a) Water in the solid state 
(b) Water in the gaseous state
(c) CO2 in liquid state 
(d) CO2 in solid state 
Ans: (d) 

Dry ice is the solid form of carbon dioxide (CO₂). It looks like ice but is not made of water.

• It is called "dry" because it does not melt into a liquid like normal ice. Instead, it changes directly from solid to gas — a process called sublimation.

• It is very cold and is used to keep things frozen (e.g., in food transport or scientific experiments).

Q7: Convert the temperature of 373°C to the Kelvin scale? 
(a) 646 K
(b) 546 K
(c) 300 K
(d) 500 K
Ans: (a)

To convert 373°C to the Kelvin scale:

Use the following formula: K = °C + 273

Now, applying the formula:

• K = 373 + 273
• K = 646

Therefore, the temperature of 373°C is equal to 646 K.

Q8: Convert the temperature of 270 K to the Celsius scale – 
(a) – 3°C
(b) – 4°C
(c) 2°C
(d) 5°C
Ans: (a)

We know that °C = K - 273.15

°C= K - 273
°C= 270 - 273
°C = -3

Q9: Plasma is the.......... state of matter  
(a) First
(b) Second
(c) Third
(d) Fourth
Ans: (d)

A plasma is a hot ionized gas consisting of approximately equal numbers of positively charged ions and negatively charged electrons. The characteristics of plasmas are significantly different from those of ordinary neutral gases so that plasmas are considered a distinct "fourth state of matter."

Q10: The process for the change of a solid directly into its vapour is called  
(a) Evaporation
(b) Precipitation
(c) Condensation
(d) Sublimation
Ans: (d)

Sublimation is the process through which a solid substance changes directly into a vapour or a gaseous state without passing through a liquid state. Dry ice is a common example of this process.

Q11: Under which of the following conditions can we boil water at room temperature? 
(a) At low pressure
(b) At moderate pressure      
(c) At very high pressure
(d) At atmospheric pressure 
Ans: (a)

Boiling occurs when the vapour pressure of a liquid equals the external pressure. At lower pressures, the boiling point of water decreases. So, if the external pressure is reduced significantly (below atmospheric pressure), water can boil at room temperature. This phenomenon can be observed in a vacuum chamber, where the pressure is significantly reduced, allowing water to boil at room temperature.

Q12: Gases have the highest rate of diffusion among all three states of matter. 
(a) True
(b) False
Ans: (a)

​Diffusion is the property of matter which is based on the motion of its particles. Diffusion occurs in gases, liquids and solids. Diffusion is fastest in gases and slowest in solids. The rate of diffusion increases on increasing the temperature of the diffusing substance.

Q13: Evaporation causes heating 
(a) True
(b) False
Ans: (b)

Evaporation causes cooling because the process requires heat energy. The energy is taken away by the molecules when they convert from liquid into gas, and this causes cooling on the original surface.

Q14: Camphor changes to a gaseous state without changing into a liquid. 
(a) True
(b) False
Ans: (a)

 It's true because camphor is sublime, and it changes directly into gas without passing through the state of liquid. The process in which a solid directly changes into a gas without passing through the state of liquid is called sublimation.

Q15: Water has a boiling point equal to 100°C. 
(a) True
(b) False
Ans: (a)

Boiling Point: The temperature at which the liquid boils and changes into gaseous state at the atmospheric pressure is called boiling point. For example, water boils at 100°C to form water vapour (at 76 cm pressure).

Q16: Evaporation is a bulk phenomenon. 
(a) True
(b) False
Ans: (b)

Evaporation is not a bulk phenomenon; it is a surface phenomenon.

• In evaporation, only the molecules at the surface of a liquid gain enough energy to escape into the air as gas.

• The entire bulk of the liquid does not participate in evaporation at once, unlike boiling, which is a bulk phenomenon where bubbles form throughout the liquid.

Q17: Intermolecular forces are maximum in solids and minimum in gases. 
(a) True
(b) False
Ans: (a)

• Intermolecular force refers to the force that exists between two or more molecules. 
• Intermolecular force of attraction is maximum in solids. 
• This is because molecules in solid remain very close to each other which allot a definite shape to the objects that are solid. 
• It is lesser in liquids and least in the gases.

Q18: Condensing is the opposite of evaporating, and freezing is the opposite of melting. 
(a) True
(b) False
Ans: (a)

• Evaporation is the process in which a liquid changes into gas, usually from the surface.

• Condensation is the opposite, where gas changes into liquid.

• Melting is the process where a solid turns into liquid.

• Freezing is the opposite, where a liquid turns into solid.

Since both pairs represent opposite processes:

Condensing ↔ Evaporating
Freezing ↔ Melting

Q19: The small volumes of gases can be put into large volumes of cylinders because of their property known as compressibility. 
(a) True
(b) False
Ans: (b)

The large volumes of gases can be put into small volumes of cylinders because of their property known as compressibility. This is possible because of the large interparticle distance and weak force of attraction between the particles of gas.

Q20: Kinetic energy of molecules is directly proportional to          
(a) Temperature
(b) Pressure         
(c) Both (a) and (b)
(d) Atmospheric pressure
Ans: (a)

According to the kinetic theory of gases, the average kinetic energy of gas molecules is directly proportional to the temperature of the gas (measured in Kelvin). This means:

• If the temperature increases, molecules move faster, so their kinetic energy increases.

• If the temperature decreases, molecules move slower, so their kinetic energy decreases.