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#### Question 1:

Which one of the following sets of phenomena would increase on raising the temperature?
(a) Diffusion, evaporation, compression of gases
(b) Evaporation, compression of gases, solubility
(c) Evaporation, diffusion, expansion of gases
(d) Evaporation, solubility, diffusion, compression of gases

On increasing temperature evaporation, diffusion and expansion of gases will increase.
Hence, the correct answer is option C.

#### Question 2:

Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identify the correct set of conditions
(a) Low temperature, low pressure
(b) High temperature, low pressure
(c) Low temperature, high pressure
(d) High temperature, high pressure

Gases can be easily liquified at low temperature and high pressure.
Hence, the correct answer is option C.

#### Question 3:

The property to flow is unique to fluids. Which one of the following statements is correct?
(a) Only gases behave like fluids
(b) Gases and solids behave like fluids
(c) Gases and liquids behave like fluids
(d) Only liquids are fluids

Liquids and gases have low intermolecular forces of attraction between their particles and thus can flow freely. Therefore, they are known as fluids.
Hence, the correct answer is option C.

#### Question 4:

During summer, water kept in an earthen pot becomes cool because of the phenomenon of
(a) diffusion
(b) transpiration
(c) osmosis
(d) evaporation

During summer, water kept in an earthen pot becomes cool because of the phenomenon of evaporation. The process of evaporation takes away the heat from the surroundings and thereby cools the water present in the earthen pot.
Hence, the correct answer is option D.

#### Question 5:

A few substances are arranged in the increasing order of ‘forces of attraction’ between their particles. Which one of the following represents a correct arrangement?
(a) Water, air, wind
(b) Air, sugar, oil
(c) Oxygen, water, sugar
(d) Salt, juice, air

The force of attraction follows the order:  Gases < Liquids < Solids
Air, Oxygen and wind are gases.
Water, juice and oil are liquids.
Sugar and salt are solids.
Hence, the correct answer is option C.

#### Question 6:

On converting 25°C, 38°C and 66°C to kelvin scale, the correct sequence of temperature will be
(a) 298 K, 311 K and 339 K
(b) 298 K, 300 K and 338 K
(c) 273 K, 278 K and 543 K
(d) 298 K, 310 K and 338 K

Celsius is converted to Kelvin using the formula

Hence the correct answer is option A.

#### Question 7:

Choose the correct statement of the following
(a) conversion of solid into vapours without passing through the liquid state is called sublimation.
(b) conversion of vapours into solid without passing through the liquid state is called vapourisation.
(c) conversion of vapours into solid without passing through the liquid state is called freezing.
(d) conversion of solid into liquid is called sublimation.

The process of conversion of solid into vapours without passing through the liquid state is called sublimation.
Hence, the correct answer is option A.

#### Question 8:

The boiling points of diethyl ether, acetone and n-butyl alcohol are 35°C, 56°C and 118°C respectively. Which one of the following correctly represents their boiling points in kelvin scale?
(a) 306 K, 329 K, 391 K
(b) 308 K, 329 K, 392 K
(c) 308 K, 329 K, 391 K
(d) 329 K, 392 K, 308 K

Celsius is converted to Kelvin using the formula

Hence, the correct answer is option C.

#### Question 9:

Which condition out of the following will increase the evaporation of water?
(a) Increase in temperature of water
(b) Decrease in temperature of water
(c) Less exposed surface area of water
(d) Adding common salt to water

Evaporation increases with an increase in temperature, as on increasing temperature the kinetic energy of the water molecules increases and they get enough energy to escape from the surface of the water and change into vapour state.
Hence, the correct answer is option A.

#### Question 10:

In which of the following conditions, the distance between the molecules of hydrogen gas would increase?
(i) Increasing pressure on hydrogen contained in a closed container
(ii) Some hydrogen gas leaking out of the container
(iii) Increasing the volume of the container of hydrogen gas
(iv) Adding more hydrogen gas to the container without increasing the volume of the container

(a) (i) and (iii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)

The distance between the particles increases by increasing the temperature and increasing the volume of the gas container.
Leakage results in a decrease in the number of gas particles in a particular volume.
Hence, the correct answer is option C.

#### Question 11:

A sample of water under study was found to boil at 102°C at normal temperature and pressure. Is the water pure? Will this water freeze at 0°C? Comment.

The melting and boiling point of pure water is 0°C and 100°C respectively. Since the given sample of water boils at 102°C, hence it is not pure water. Thus, it will freeze below 0°C.

#### Question 12:

A student heats a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time. Which of the following Figure would correctly represent the result? Justify your choice.

Ice and water are in equilibrium, the temperature would be zero. On heating the mixture, energy supplied is utilised in melting the ice and temperature does not change till the ice melts because of latent heat of fusion. On further heating, the temperature of the water would increase.
Hence, the correct answer is option D.

#### Question 13:

Fill in the blanks:
(a) Evaporation of a liquid at room temperature leads to a _________ effect.
(b) At room temperature the forces of attraction between the particles of solid substances are _________ than those which exist in the gaseous state.
(c) The arrangement of particles is less ordered in the _________ state. However, there is no order in the _________ state.
(d) _________ is the change of solid state directly to vapour state without going through the _________ state.
(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called _________.

(a) cooling
(b) stronger
(c) liquid, gaseous
(d) Sublimation, liquid
(e) evaporation

#### Question 14:

Match the physical quantities given in column A to their SI units given in column B :

 (A) (B) (a) Pressure (i) cubic metre (b) Temperature (ii) kilogram (c) Density (iii) pascal (d) Mass (iv) kelvin (e) Volume (v) kilogram per cubic metre

(a)- (iii)
(b)-(iv)
(c)-(v)
(d)-(ii)
(e)-(i)

#### Question 15:

The non SI and SI units of some physical quantities are given in column A and column B respectively. Match the units belonging to the same physical quantity:

 (A) (B) (a) degree celsius (i) kilogram (b) centimetre (ii) pascal (c) gram per centimetre cube (iii) metre (d) bar (iv) kelvin (e) milligram (v) kilogram per metre cube

(a)-(iv)
(b)-(iii)
(c)-(v)
(d)-(ii)
(e)-(i)

#### Question 16:

‘Osmosis is a special kind of diffusion’. Comment.

In osmosis, the solvent particles move from a region of high concentration towards a region of low concentration through a semi-permeable membrane. Hence, osmosis is a special case of diffusion.

#### Question 17:

Classify the following into osmosis /diffusion
(a) Swelling up of a raisin on keeping in water.
(b) Spreading of virus on sneezing.
(c) Earthworm dying on coming in contact with common salt.
(d) Shrinking of grapes kept in thick sugar syrup.
(e) Preserving pickles in salt.
(f) Spreading of smell of cake being baked through out the house.
(g) Aquatic animals using oxygen dissolved in water during respiration.

(a) osmosis
(b) diffusion
(c) osmosis
(d) osmosis
(e) osmosis
(f) diffusion
(g) diffusion

#### Question 18:

Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.

When ice melts it absorbs heat from the surrounding, in the form of latent heat of fusion and changes its state. Due to which ice causes cooling effect. On the other hand, when water changes into steam it absorbs heat energy from the water and changes its state into steam, Hence, the water molecules in steam have higher kinetic energy and cause more severe burns.

#### Question 19:

Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Comment.

The temperature of both boiling water and steam is 100 ºC but the steam has more energy than that of the water as steam contains the latent heat of vaporisation. Hence, steam is hotter than boiling water.

#### Question 20:

A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 0°C). If you could measure the temperature of the content of the tumbler, which of the following graphs Fig.1.2) would correctly represent the change in its temperature as a function of time.

Figure (a) represents the change in temperature with respect to time correctly. The temperature of water decreases up to 0°C which is the freezing point of water, then remains constant for some time, as the water gets converted to ice and then the temperature decreases further.

#### Question 21:

Look at Figure and suggest in which of the vessels A,B, C or D the rate of evaporation will be the highest? Explain.

Evaporation will be highest in C.
The rate of evaporation increases with the increase in surface area and wind. Beaker C has a larger surface area along with the wind factor contributed by the fan above the beaker. Hence, it will show highest rate of evaporation amongst the given options.

#### Question 22:

(a) Conversion of solid to vapour is called sublimation. Name the term used to denote the conversion of vapour to solid.
(b) Conversion of solid state to liquid state is called fusion; what is meant by latent heat of fusion?

(a) Conversion of vapour to solid is known as deposition.
(b)  The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion.

#### Page No 11:

The mixture of ammonium chloride and naphthalene can be separated by the solubility process. Ammonium chloride is soluble in water whereas naphthalene is not.
1. Add the mixture in water.
2. Stir it for 10 minutes so that ammonium chloride is dissolved in water completely.
3. Filter it using filter paper. Collect the filtrate in a beaker.
4. Now you have naphthalene on the filter paper and aqueous solution of ammonium chloride is in the beaker.
5. Evaporate the water carefully from the solution.
6. After all the water is evaporated, recrystallize to obtain the pure ammonium chloride crystals.

#### Question 24:

It is a hot summer day, Priyanshi and Ali are wearing cotton and nylon clothes respectively. Who do you think would be more comfortable and why?

Priyanshi will be more comfortable as she is wearing cotton clothes.
Cotton clothes have tiny pores which allow the air to pass through them letting the sweat to evaporate. When sweat will evaporate, it will take up the heat from the surrounding i.e., the human body and hence causing the cooling effect.
On the other hand, Ali will not be comfortable as he is wearing nylon clothes.

#### Question 25:

You want to wear your favourite shirt to a party, but the problem is that it is still wet after a wash. What steps would you take to dry it faster?

The shirt can be dried faster by evaporating water which can be done in many ways:
1. Allowing the shirt under a fan of high speed. Evaporation increases with an increase in wind speed.
2. Using hot iron for the shirt. Evaporation increases with an increase in temperature.
3. Spreading out the shirt under the sunlight or in an open area. Evaporation increases with an increase in surface area.

#### Question 26:

Comment on the following statements:
(a) Evaporation produces cooling.
(b) Rate of evaporation of an aqueous solution decreases with increase in humidity.
(c) Sponge though compressible is a solid.

(a) When liquid converts into the gaseous phase, it needs energy in the form of heat. The heat is absorbed by the surrounding. When heat is lost from surroundings it leads to a decrease in temperature.

(b) A sponge is solid but is still compressible because of the numerous air cavities inside it.

#### Question 27:

Why does the temperature of a substance remain constant during its melting point or boiling point?