Matter In Our Surroundings - 1 - UPSC Sci & Tech Free MCQ Test with solutions

• Option A: Boiling Point of Water - 273 K
  This is incorrect because the boiling point of water is 373 K, not 273 K. 273 K is the melting point of ice.
• Option B: Melting Point of Ice - 373 K
  This is incorrect because the melting point of ice is 273 K, not 373 K. 373 K is the boiling point of water.
• Option C: Latent Heat of Fusion - Energy required to change 1 kg of solid to liquid
  This is correct. The latent heat of fusion is defined as the amount of heat energy required to change 1 kg of a solid into a liquid at atmospheric pressure at its melting point.
• Option D: Latent Heat of Vaporisation - Temperature at which a liquid starts boiling
  This is incorrect. The latent heat of vaporisation is the amount of heat energy required to change 1 kg of a liquid into a gas at atmospheric pressure at its boiling point. The temperature at which a liquid starts boiling is known as its boiling point.

Therefore, the correctly matched pair is Option C: Latent Heat of Fusion - Energy required to change 1 kg of solid to liquid.

Liquefaction of gases is the process of converting a gas into a liquid. This can be achieved through the following methods:

• Increasing pressure: Applying pressure can force gas molecules closer together, facilitating the transition to a liquid state.
• Decreasing temperature: Lowering the temperature reduces the energy of the gas molecules, promoting condensation into a liquid.

In summary, both increasing pressure and decreasing temperature are essential for the liquefaction of gases.

Particles of matter intermix on their own with each other by getting into the spaces between the particles.

Particles of matter naturally mix through a process called diffusion. This occurs when:

• Particles move from areas of high concentration to low concentration.
• The spaces between particles allow them to intermingle freely.
• This process continues until the particles are evenly distributed.

Diffusion occurs faster under certain conditions, particularly at high temperatures. Here are the key points:

• High temperature increases the kinetic energy of particles.
• With more energy, particles move rapidly and mix more easily.
• As temperature rises, the attractive forces between particles are overcome.
• This results in a quicker diffusion process.

Factors affecting the rate of evaporation:

• Surface area: More surface area leads to increased evaporation.
• Temperature: Higher temperatures facilitate faster evaporation.
• Wind speed: Increased wind speed enhances evaporation by removing water vapour.
• Humidity: If the amount of water in the air is already high, the rate of evaporation decreases.

Therefore, the factor that does not affect the rate of evaporation is insoluble heavy impurities.

• Option A: Panch Tatva - Five Basic Elements: This is correctly matched. The Panch Tatva includes air, earth, fire, sky, and water, which are considered the fundamental elements of all matter.
• Option B: SI unit of mass - Litre: This is incorrect. The SI unit of mass is kilogram (kg), while litre is a unit of volume.
• Option C: Particles of matter - Continuous: This is incorrect. Matter is made up of discrete particles, not a continuous substance.
• Option D: SI unit of volume - metre: This is incorrect. The SI unit of volume is cubic metre (m³), not metre.

Explanation:

• The Assertion that evaporation causes cooling in an open vessel is correct. When liquid evaporates, the particles of the liquid absorb energy from the surroundings to compensate for the energy lost during the process. This absorption of energy results in a cooling effect, making the surroundings feel colder.
• The Reason provided explains this phenomenon accurately. Energy absorption during evaporation is a key factor that leads to the cooling effect. Therefore, the Reason is a correct explanation for the Assertion.

Conclusion:

• Both the Assertion and Reason are true, and the Reason accurately explains why the Assertion is valid. Hence, Option A is the correct answer choice.

Gases are highly compressible because their particles are far apart with large empty spaces between them.
When pressure is applied, these spaces get reduced, so gases can be compressed easily.

Random movement (option C) explains diffusion and pressure, not compressibility.

• Solids have:

  • A definite shape (they do not change shape unless forced).

  • A definite volume (they do not expand to fill a container).

Why other options are incorrect:

• B) Indefinite shape and volume → This is true for gases, not solids.

• C) Indefinite shape but definite volume → This is true for liquids.

• D) Definite shape but indefinite volume → Solids do not have indefinite volume.

• Assertion (A) is true: Water droplets form on the outer surface of a glass containing ice-cold water because the cold temperature of the glass causes moisture in the air to condense.
• Reason (R) is false: Water does not evaporate from the glass and condenses on the outside. Instead, the moisture in the surrounding air condenses on the cooler surface of the glass.
• Therefore, the correct option is C: The assertion is true, but the reason is false.