Question 1.
Riya adds a spoonful of sugar to a glass of water and stirs it. After a few minutes, the sugar disappears, but the water level does not increase noticeably.
Which statement best explains this observation?
A. Sugar particles evaporate into the air.
B. Sugar particles occupy the empty spaces between water particles.
C. Water particles become smaller after stirring.
D. Sugar loses its mass when dissolved.
Answer: B
Explanation:
The observation shows that matter consists of tiny particles with spaces between them. Sugar particles fit into the spaces between water particles.
Question 2.
A company wants to store a large amount of oxygen in a cylinder for medical use. Engineers compress the oxygen before filling the cylinder.
Why can oxygen be compressed easily while water cannot?
A. Oxygen particles have much larger spaces between them than water particles.
B. Oxygen particles are heavier than water particles.
C. Water particles move faster than oxygen particles.
D. Oxygen has a lower temperature than water.
Answer: A
Explanation:
Gas particles are far apart, so they can be brought closer together by applying pressure. Liquid particles already have very little empty space.
Question 3.
A teacher sprays perfume at one corner of a classroom. After a short time, students sitting at the back of the room can also smell it.
Which conclusion is supported by this observation?
A. Air particles are stationary.
B. Fragrance particles move only upward.
C. Gas particles are continuously moving and spread by diffusion.
D. Perfume becomes lighter after spraying.
Answer: C
Explanation:
The fragrance spreads because perfume particles mix with air due to the continuous random motion of gas particles.
Question 4.
A student heats an ice cube in a beaker. After some time, the ice changes into water.
Which statement correctly explains why this change occurs?
A. Heating increases the vibrations of particles until they overcome the attractive forces.
B. Heating creates new particles inside the ice.
C. Heating removes the mass of the ice.
D. Heating decreases the motion of particles.
Answer: A
Explanation:
Heat energy increases the kinetic energy of particles. When the particles vibrate sufficiently to overcome the attractive forces, the solid melts into a liquid.
Question 5.
Three containers contain substances X, Y, and Z.
X has a definite shape and definite volume.
Y has a definite volume but takes the shape of its container.
Z has neither a definite shape nor a definite volume.
Which option correctly identifies X, Y, and Z?
A. X–Gas, Y–Solid, Z–Liquid
B. X–Liquid, Y–Gas, Z–Solid
C. X–Solid, Y–Liquid, Z–Gas
D. X–Solid, Y–Gas, Z–Liquid
Answer: C
Explanation:
Solids have a definite shape and volume.
Liquids have a definite volume but no fixed shape.
Gases have neither a definite shape nor a definite volume.
These properties arise from differences in particle arrangement, inter-particle spacing, and the strength of attractive forces
Question 6.
why are liquids able to flow while solids cannot?
Answer:
Liquids flow because their particles have enough space to slide past one another. In solids, particles are tightly packed and cannot move freely.
Question 7.
Compare the arrangement of particles in solids, liquids, and gases.
Answer:
| State | Particle Arrangement |
| ------ | ------------------------------------------------------- |
| Solid | Tightly packed with very little space between particles |
| Liquid | Loosely packed with moderate space between particles |
| Gas | Very far apart with large spaces between particles |
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Question 8
Why do solids have a definite shape and definite volume?
Answer:
Solids have strong intermolecular forces and very little space between particles. The particles remain fixed in their positions, giving solids a definite shape and volume.
Question 9
Why are gases highly compressible whereas liquids are not?
Answer:
Gases contain large spaces between their particles, allowing them to be compressed easily. Liquids have much smaller spaces between particles, so they cannot be compressed significantly.
Question 10.
Describe the particle arrangement and properties of solids.
Answer:
* Particles are tightly packed.
* Strong force of attraction.
* Definite shape and volume.
* Rigid and incompressible.
Question 11.
Describe the particle arrangement and properties of liquids.
Answer:
* Particles are loosely packed.
* Moderate force of attraction.
* Definite volume but no definite shape.
* Can flow and take the shape of the container.
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Question 12.
Describe the particle arrangement and properties of gases.
Answer:
* Particles are very far apart.
* Negligible force of attraction.
* No definite shape or volume.
* Fill the entire container.
Question 13.
Explain with an example how the same substance can exist in all three states.
Answer:
Water exists as:
* Ice (solid)
* Liquid water (liquid)
* Water vapour (gas)
Changing temperature changes the state of the same substance.
Question 14.
Why does a solid melt when heated?
Answer:
Heating provides energy to the particles, increasing their vibrations. Eventually, the particles overcome the attractive forces holding them in fixed positions and begin to move freely, causing the solid to melt.
Question 15.
What happens to the movement of particles when temperature increases?
Answer:
As temperature increases, particles gain kinetic energy and move faster.
Question 16
Why do gases have neither a definite shape nor a definite volume?
Answer:
Gas particles move freely in all directions and spread throughout the available space, so gases have neither a fixed shape nor a fixed volume.
Question 17
Which state of matter has the maximum inter-particle space? Explain.
Answer:
Gases have the maximum inter-particle space because their particles are very far apart and experience negligible attractive forces.