Test: Matter In Our Surroundings - 2 - Grade 9 MCQ

• a) Matter is made up of particles – Correct. All matter consists of tiny particles (atoms, molecules, or ions).

• b) Particles of matter are always in a state of motion – Correct. Particles possess kinetic energy and are constantly moving (vibrating in solids, moving freely in gases).

• c) Matter is continuous in nature – Incorrect. Matter is not continuous; it is made up of discrete particles with empty spaces between them. This was disproven by the kinetic theory of matter.

• d) Particles of matter attract each other – Correct. Intermolecular forces (like van der Waals forces) exist between particles.

Kelvin is the SI Unit of measurement of temperatures. It is represented with the Unit Kelvin 'K'.

Temperatures can be converted from Celsius to Kelvin by adding 273 to the Celsius Scale.

We have been given 3 temperatures here which are in the Celsius Scale.

25°C, 38°C and 66°C

To convert all of them to the Kelvin Scale, add 273 to all of them.

25 + 273 = 298 K
38 + 273 = 311 K
66 + 273 = 339 K

For liquefying gas, the correct conditions involve:

• Low temperature - This reduces the kinetic energy of gas molecules, making them easier to condense.
• High pressure - This forces gas molecules closer together, promoting liquefaction.

Combining low temperature and high pressure is ideal for converting gas to liquid.

• Fluids are materials that can flow, which includes both gases and liquids.
• Gases, like air, can change shape and fill their containers, demonstrating fluid behavior.
• Liquids, such as water, also flow and take the shape of their containers.
• Solids, on the other hand, maintain a fixed shape and do not flow, thus are not considered fluids.

The correct order of forces of attraction is:
- Air < Water < Sugar
Explanation:
- Air has the weakest forces of attraction among the options given.
- Water exhibits stronger forces of attraction compared to air due to hydrogen bonding.
- Sugar demonstrates the strongest forces of attraction in this sequence, likely due to its molecular structure and intermolecular forces.
This order reflects the varying degrees of intermolecular forces present in these substances, with sugar having the highest and air having the lowest.

• Increase in temperature of water: Higher temperatures provide more energy to water molecules, causing them to move faster and escape into the air, which increases evaporation.
• Decrease in temperature of water: Cooler temperatures reduce molecular movement, leading to slower evaporation rates.
• Less exposed surface area: A smaller surface area limits the number of molecules that can escape, reducing evaporation.
• Adding common salt to water: Salt increases the boiling point and decreases the rate of evaporation as it binds with water molecules.

Option A: Incorrect. Vaporisation refers to the conversion of a liquid into vapours, not directly from solid to vapours.
Option B: Correct. Sublimation is the process where a solid changes directly into vapours without passing through the liquid state.
Option C: Incorrect. Condensation is the process where vapours change into a liquid, not directly into a solid.
Option D: Incorrect. Fusion refers to the process of melting, where a solid changes into a liquid, not directly into vapours.

Evaporation ,diffusion and expansion of gases increase the temperature. Evaporation rate increases because of increasing temperature ,kinetic energy of molecules increases , so the molecules present at the surface of the liquid leave the surface quickly and go into the vapour state.

• Compressibility Increases: As a solid melts, its structure becomes less rigid, allowing the liquid to be compressed more easily.
• Interparticle Forces Decrease: In solids, particles are tightly packed with strong forces. When melting occurs, these forces weaken, allowing particles to move more freely.
• Kinetic Energy Increases: The heat energy added during melting causes particles to vibrate and move faster, leading to increased kinetic energy.

The heat  energy  required  to change  the state  of unit mass of  a substance  is called  latent  heat.  As the given solid is of unit mass  ( 1 kg)   and  we have  to change   its state into  liquid  , therefore  heat  needed will  be specific  latent heat of  fusion.

Sublimation is the process where a solid transitions directly into a gas without passing through the liquid phase. Let's evaluate each option:

• a) Ammonium chloride: Ammonium chloride (NH₄Cl) undergoes sublimation. When heated, it decomposes into ammonia (NH₃) and hydrogen chloride (HCl) gases, which can recombine into a solid upon cooling. Undergoes sublimation.
• b) Sodium chloride: Sodium chloride (NaCl), or common salt, does not undergo sublimation. It has a very high melting point (around 801°C) and boiling point (1413°C), and when heated, it melts into a liquid before vaporizing. Does not undergo sublimation.
• c) Solid carbon dioxide: Solid carbon dioxide (CO₂), also known as dry ice, sublimates at -78.5°C under standard pressure, turning directly into CO₂ gas without melting. Undergoes sublimation.
• d) Iodine: Iodine (I₂) sublimates when heated. At room temperature, it can slowly sublime, and when heated gently, it turns directly into a purple vapor without melting. Undergoes sublimation.

Conclusion: Among the options, b) Sodium chloride does not undergo sublimation, as it melts into a liquid before vaporizing, unlike the others which transition directly from solid to gas.

• The SI unit of temperature is indeed kelvin, which measures thermal energy.
• The correct SI unit of pressure is Pascal, not Newton. Pascal measures force per unit area, while Newton measures force.
• Density is measured in kg/m³, which indicates mass per unit volume.
• One litre is equivalent to 1000 cm³ or 1 dm³, demonstrating the relationship between these volume measurements.

Solids do not flow because:

• The particles are held together by strong intermolecular forces.
• These forces prevent particles from moving past one another.

This is why solids maintain a fixed shape and volume.