Matter in Our Surroundings Important Questions.

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1. Q1Medium

   Which of the following materials demonstrates **sublimation** when heated?

   • A.Ice
   • B.Ammonium chloride (NH₄Cl)
   • C.Sugar
   • D.Salt
   Answer: Ammonium chloride (NH₄Cl)

   Explanation: Sublimation is the direct conversion of a solid to a gas without passing through the liquid state. Ammonium chloride is a common example of a substance that sublimes when heated.

2. Q2Medium

   What is the primary reason why a rubber band can change its shape when stretched but still return to its original form?

   • A.It is a liquid
   • B.It is a gas
   • C.It has elastic intermolecular forces
   • D.It is a mixture
   Answer: It has elastic intermolecular forces

   Explanation: Rubber bands exhibit elasticity because their molecular chains can stretch and return to their original configuration when the force is removed, provided the force is not excessive.

3. Q3Medium

   Which of the following substances would have the highest rate of evaporation in a dry, windy environment?

   • A.Water
   • B.Alcohol
   • C.Honey
   • D.Oil
   Answer: Alcohol

   Explanation: Alcohol evaporates faster than water due to its lower boiling point and weaker intermolecular forces, allowing its particles to escape into the vapor phase more readily.

4. Q4Medium

   Why does ice float on water?

   • A.Ice is heavier than water
   • B.Ice is more compressible
   • C.The hydrogen bonds in ice create a less dense structure
   • D.Ice is a gas in solid form
   Answer: The hydrogen bonds in ice create a less dense structure

   Explanation: Ice is less dense than liquid water because its solid structure has more open space due to hydrogen bonding, causing it to float.

5. Q5Medium

   What is the boiling point of water at standard atmospheric pressure?

   • A.323 K (50°C)
   • B.373 K (100°C)
   • C.273 K (0°C)
   • D.473 K (200°C)
   Answer: 373 K (100°C)

   Explanation: The boiling point of water is defined as the temperature at which liquid water converts to vapor at standard atmospheric pressure, which is 100°C or 373 K.

6. Q6Medium

   Which of the following activities demonstrates the principle of **latent heat of vaporization**?

   • A.Melting of ice
   • B.Evaporation of sweat from skin on a hot day
   • C.Freezing of water
   • D.Condensation of steam
   Answer: Evaporation of sweat from skin on a hot day

   Explanation: Latent heat of vaporization is the energy required to convert a liquid into a vapor without changing its temperature. Sweat evaporating from the skin absorbs heat from the body, cooling it down.

7. Q7Medium

   Which of the following materials is least likely to exhibit diffusion in water?

   • A.Salt
   • B.Sugar
   • C.Sand
   • D.Alcohol
   Answer: Sand

   Explanation: Sand particles are large and do not dissolve or disperse in water, unlike substances like salt or sugar, which exhibit diffusion due to their smaller particle size.

8. Q8Medium

   What happens to the temperature of water when it undergoes a phase change from liquid to gas at its boiling point?

   • A.The temperature increases
   • B.The temperature decreases
   • C.The temperature remains constant
   • D.The temperature fluctuates randomly
   Answer: The temperature remains constant

   Explanation: During a phase change, the added heat energy is used to overcome intermolecular forces, converting liquid to gas without raising the temperature.

9. Q9Medium

   Which of the following is an example of a **bulk phenomenon**?

   • A.Evaporation of water from a puddle
   • B.Melting of ice
   • C.Boiling of water
   • D.Sublimation of dry ice
   Answer: Boiling of water

   Explanation: Boiling is a bulk phenomenon where particles throughout the liquid gain enough energy to transition into vapor simultaneously.

10. Q10Medium

    Why does water in an earthen pot become cooler during summer?

    • A.The pot absorbs heat from the surroundings
    • B.The water inside freezes
    • C.Due to the process of evaporation from the porous pot walls
    • D.The pot reflects sunlight
    Answer: Due to the process of evaporation from the porous pot walls

    Explanation: The porous earthen pot allows water to evaporate through its surface, absorbing heat from the water and cooling it down.

11. Q11Medium

    What is the primary reason why acetone feels cold when applied to the skin?

    • A.Acetone is a gas at room temperature
    • B.Evaporation of acetone absorbs heat from the skin
    • C.Acetone conducts heat away from the skin
    • D.Acetone reacts chemically with skin
    Answer: Evaporation of acetone absorbs heat from the skin

    Explanation: Acetone evaporates quickly from the skin, taking heat away from the body and creating a cooling sensation.

12. Q12Medium

    Which of the following materials is best suited for wearing in summer due to its ability to allow evaporation?

    • A.Polyester
    • B.Wool
    • C.Cotton fabric
    • D.Leather
    Answer: Cotton fabric

    Explanation: Cotton allows sweat to evaporate easily, which helps in cooling the body by absorbing heat from the skin.

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