Test: Matter In Our Surroundings - 1 - Class 9 MCQ

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 in which a gas is liquified to change its state from gas to liquid. A gases can be liquified by increasing pressure and reducing the temperature.

The random movement of microscopic particles in a fluid is known as Brownian motion. This phenomenon was first observed by Robert Brown and is a result of continuous collisions between the particles and molecules in the surrounding medium.

Particles of matter intermix on their own with each other by getting into the spaces between the particles, which is known as diffusion.

Diffusion becomes faster at high temperatures. This is because, at higher temperatures, the particles of matter gain more kinetic energy, allowing them to move more rapidly and intermix more quickly. As temperature increases, the kinetic energy overcomes the forces of attraction between particles, facilitating faster diffusion.

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 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. According to early Indian philosophers, the Panch Tatva (five basic elements) include air, earth, fire, sky, and water.
• Option B: SI unit of mass - Litre: This is incorrect. The SI unit of mass is kilogram (kg), not litre. Litre is a unit of volume.
• Option C: Particles of matter - Continuous: This is incorrect. Modern science classifies matter as being made up of particles, which are not continuous.
• Option D: SI unit of volume - metre:  This is incorrect

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 due to the random movement of their particles, which allows them to be easily compressed into smaller volumes. This property is a result of the high speed and random motion of gas particles, enabling gases to exert pressure equally in all directions.

- 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 condense 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.