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Q1. Give the full form of LPG and CNG


  • LPG stands for Liquified Petroleum Gas and
  • CNG stands for Compressed Natural Gas.

Q2. Why is the diffusion of one solid into another a slow process? What could be an example of diffusion of one solid in another. Give examples for the same.


Particles in solids are packed tightly and the particles do not move from their position. They only vibrate from their own position. This makes it difficult for one solid to diffuse into another and thus the process is slow.

Alloys of metals are the best example for diffusion of a solid in another solid.

Example :

  • Brass is an alloy of Copper and Zinc
  • Bronze is an alloy of copper and tin 
  • Nichrome is an alloy Nickel and Chromium

Carbon and Iron particles packed tightly at solid state-Teachoo-01.jpg

Q3. Why is air used to inflate tyres?


Air has the property of high compressibility under some extent of pressure. Air also has pressure and makes it easy to drive smoothly on roads.

Air is used to inflate tyres due to its property of compressibility under pressure-Teachoo-01.jpg

Q4. Why is steel used while laying railway lines?


Steel is an alloy and has greater strength. This property makes the railway lines stronger when made of steel.

Moreover, steel expands during the summer months but the expansion only results in increase in size and no change in shape.

The alloy steel has great strength thus used to lay railway lines-Teachoo-01.jpg

Q5. Honey is more viscous than water. Give reason


Viscosity is a measure of a fluid's resistance to flow . Particles of matter have a certain force of attraction between them. This force of attraction between particles of honey is more than that in water . This makes honey more viscous than water.

Q6. Explain ‘Osmosis is a special kind of Diffusion’. State if the following example is osmosis or diffusion:

  1. Swelling up of raisins while keeping in water
  2. Spreading of virus on sneezing
  3. Earthworm dying on coming into contact with air
  4. Shrinking of grapes when kept in sugar syrup
  5. Preserving of pickles in salt
  6. Smell of food being cooked
  7. Aquatic animals using dissolved oxygen in water to breathe

Osmosis is a special kind of diffusion-Teachoo-01.jpg


Diffusion is the movement of particles from a region of high concentration to low concentration without the presence of a membrane . It can be the movement of solute as well as solvent molecules.

Osmosis is the movement of particles from a region of high concentration to low concentration across a semipermeable membrane . Thus Osmosis is a special kind of Diffusion. 

Only the solvent molecules can pass through.

  1. Swelling up of raisins while keeping in water - Osmosis
  2. Spreading of virus on sneezing - Diffusion
  3. Earthworm dying on coming into contact with air - Osmosis
  4. Shrinking of grapes when kept in sugar syrup - Osmosis
  5. Preserving of pickles in salt - Osmosis
  6. Smell of food being cooked - Diffusion
  7. Aquatic animals using dissolved oxygen in water to breathe - Diffusion


Q7. What is Brownian Motion? What causes the zig-zag motion of pollen grains when added to a glass of water?


The random motion of larger visible particles due to the motion of the smaller invisible particles of matter is known as Brownian motion .

Though the water molecules are very small and invisible to naked eyes, their presence and movement are visible through the movement of the visible larger pollen grains. The water molecules that move at a fast pace strike against the pollen grains resulting in the zig-zag motion of pollen grains. 

Brownian motion resulting in zig-zag motion of pollen grains in water-Teachoo-01.jpg

Q8. 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



(c) Evaporation, diffusion, expansion of gases 


Reason : As the temperature increases, the kinetic energy of the particles increases. 

  • Evaporation : As the kinetic energy increases the particles can break free from the rest of the liquids with greater ease.
  • Diffusion : With the increase in kinetic energy, the particles of one matter can diffuse into another easily.
  • Expansion of gases : With the increase in temperature, gases expand

Q9. 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



(c) Low temperature, high pressure


Reason : Under conditions of low temperature and high pressure, the particles of the gas come closer to each other. This enables us to liquefy gases.

Q10. ln 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)


(c) (ii) and (iii) 


Explanation : (ii) When some Hydrogen gas leaks out of the container, the remaining gas spreads out to occupy the entire space. When a lesser amount of gas occupies the same space, the space between the particles increases. 

(iii) When the volume of the container is increased the same amount of gas has a larger amount of space to occupy . So the gas spreads out to fill the whole space. Thus the space between the molecules increases. 

Q11. 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.



Pure water boils at 100 °C. The sample of water boils at 102°C at normal temperature and pressure. Since it boils at a temperature higher than pure water, the sample of water is not pure. 

Also, the water will not freeze at 0°C because it is impure. It will freeze at a temperature below 0°C.

Q12. 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 graphs would correctly represent the result? Justify your choice.


(d) Initially ice and water are at equilibrium, so the temperature is 0°C. On heating ice, the heat energy is used in complete conversion of ice to water. This is called the latent heat of fusion. At this point, there is no increase in temperature. Once all the ice is melted, the temperature slowly rises. Thus graph (d) is correct.

Temperature of ice and water being recorded to observe the constant temperature reading due to latent heat of fusion-Teachoo-01.jpg

Q13. Match the physical quantities given in column A to their SI units given in column B.


Column A

Column B

a.       Pressure

i.                     Cubic meter

b.       Temperature

ii.                   Kilogram

c.       Density

iii.                 Pascal

d.       Mass

iv.                 Kelvin

e.       Volume

v.                   Kilogram per cubic meter



  1. →  iii
  2. → iv
  3. → v
  4. → ii
  5. → i

Q14. Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.



Ice and Steam are both forms of water. Ice is formed by freezing water at lower temperatures. The energy in ice is low. When we touch ice, the heat from our body is transferred to the ice and heat is transferred from regions of higher temperature to that of lower temperature. Since there is reduction of heat in our body, there is a cooling effect. 

Steam on the other hand is formed when water is heated at boiling point and converts to vapours. The vapours possess very high energy. The high energy of steam in terms of heat causes severe burns when we touch. 


Q15. Look at the figure and suggest in which of the vessels A, B, C or D the rate of evaporation will be highest? Explain.



Figure C shows the highest rate of evaporation.



Rate of evaporation increases with an increase in surface area. Also, the rate of evaporation increases with an increase in wind speed. In figure C, the surface area exposed is high and The fan increases the wind speed. 

On comparing A and D, though the surface area in A is high, the wind speed is relatively less in A. B  has less surface area exposed to the open, so the rate of evaporation is less. D is not exposed for evaporation.

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo