States Of Matter - Class 9 Science Free MCQ Practice Test with solutions

The three primary states of matter are solid, liquid, and gas. Each state has distinct properties:

• Solids have a definite shape and volume. The particles are closely packed, resulting in fixed boundaries.
• Liquids have a definite volume but take the shape of their container. The particles are less tightly packed than in solids, allowing them to flow.
• Gases have neither a definite shape nor volume. The particles are far apart and move freely, filling the available space.

These states arise from variations in the characteristics of the particles:

• The forces of attraction between particles are strongest in solids, moderate in liquids, and weakest in gases.
• The kinetic energy of particles increases from solids to gases, affecting their movement and arrangement.

Solids have distinct characteristics that set them apart from other states of matter. Here are the key features:

• Fixed Shape: Solids maintain a definite shape and do not change unless a significant force is applied.
• Fixed Volume: They occupy a specific volume and do not expand or contract easily.
• Packed Particles: The particles in solids are tightly packed in a fixed arrangement, making them rigid.
• Resistance to Change: While solids can break under excessive force, they resist changes in shape.

Examples of solids include: Rubber Bands, Crystals and Wood.

A rubber band is a flexible material that can change its shape when a force is applied. Unlike rigid materials such as wood or stone, which maintain their shape, a rubber band can stretch and then return to its original form.

• A rubber band is flexible and can be stretched.
• When released, it regains its original shape.
• Rigid materials like wood and stone do not change shape easily.

In summary, a rubber band is unique among common materials because it can adapt its shape under force, demonstrating its elasticity.

When a sponge is compressed, the following occurs:

• The air trapped inside the sponge is forced out.
• This temporarily reduces the sponge's volume.
• As a result, the sponge becomes denser and easier to handle.

In summary, compressing a sponge expels air, allowing it to be compacted.

The correct answer is C: Gas.

• Particle Movement: In a gas, particles move freely and rapidly in all directions.
• Particle Spacing: Gases have the maximum space between particles compared to solids and liquids.
• Kinetic Energy: Gas particles possess higher kinetic energy, allowing them to overcome attractive forces easily.
• Shape and Volume: Gases do not have a fixed shape or volume; they expand to fill their container.
• Diffusion: Due to the large spaces, gases diffuse quickly, mixing with other gases.

The particles in liquids can move past each other, which enables them to change shape based on the container they occupy. Here are some key points:

• Movement: The particles in liquids have more space between them compared to solids, allowing for free movement.
• Shape: Liquids do not have a fixed shape; they adapt to the shape of their container.
• Volume: While liquids take the shape of their container, they maintain a fixed volume.
• Fluidity: Because they can flow and change shape, liquids are classified as fluids.

The correct answer is:

d) Solids, Liquids, and Gases

Explanation:

All three states of matter—solids, liquids, and gases—can diffuse in water, but they must first dissolve or disperse into the liquid:

1. Gases (e.g., oxygen or CO₂ dissolving in water).

2. Liquids (e.g., alcohol mixing with water).

3. Solids (e.g., salt or sugar dissolving into ions/molecules that then diffuse).

While solids must dissolve first, their particles do diffuse in water after breaking down. Thus, all three can diffuse, making (d) the most complete and accurate choice.

Gases are highly compressible due to the following reasons:

• The particles in gases are spread far apart.
• They can be pushed closer together when pressure is applied.
• This property allows large volumes of gas to be stored in small containers, such as cylinders for LPG or oxygen.

In contrast, solids and liquids have particles that are much closer together, making them less compressible. When you try to compress a solid or liquid, it does not change volume significantly.

Additionally, in the gaseous state, particles move randomly and at high speed, which contributes to their ability to fill any available space and exert pressure on the walls of their container.

The smell of food reaches us quickly because:

• The particles of aroma mix with air particles.
• In gases, particles move at a high speed.
• This rapid movement allows smells to travel over long distances.
• Compared to solids and liquids, gases diffuse much faster.

This is why we can smell hot food from several metres away almost instantly.

Gas particles move randomly and collide with the walls of their container, which leads to the exertion of pressure. This can be explained as follows:

• The particles are in constant motion, moving at high speeds.
• As they collide with the walls, they apply force on the surface.
• This force per unit area is what we measure as pressure.

Thus, the main reason for the pressure exerted by gases is their random movement and the collisions with the container walls.

In gases, particles move randomly and at high speeds. This rapid movement allows them to:

• Spread out and fill any container.
• Collide with each other and the walls of the container.
• Exert pressure on the walls, which is a result of these collisions.

The gaseous state is characterised by:

• High kinetic energy of particles.
• Minimal forces of attraction between particles.
• A lack of ordered arrangement, leading to random motion.

The melting point of ice is 273.15 K, which is equivalent to 0°C. This is the temperature at which solid ice transforms into liquid water.

Key points about the melting process:

• The melting point indicates the strength of the forces between the particles in a solid.
• During melting, the temperature remains constant until all the ice has converted to water.
• Heat energy supplied during this process is used to overcome the attractive forces between particles.

This process is also referred to as fusion.

The latent heat of fusion refers to the amount of heat energy needed to convert a solid into a liquid at its melting point, without changing its temperature. Here are some key points:

• The process occurs at the melting point of the solid.
• During this change, the temperature remains constant.
• The heat energy is used to overcome the forces of attraction between the particles.
• For example, when ice melts, it absorbs heat without an increase in temperature.
• The latent heat of fusion is typically measured in joules per kilogram (J/kg).

In summary, the latent heat of fusion is essential for understanding how solids transition to liquids while maintaining a stable temperature.

The correct answer is:

b) Boiling is a bulk phenomenon where particles gain enough energy to change into a vapour 

Explanation:

• Boiling is a bulk phenomenon, which means it happens throughout the liquid, not just at the surface.
• When a liquid reaches its boiling point, the particles inside the liquid gain enough energy to overcome intermolecular forces and turn into vapour.
• Options (a) and (c) are incorrect because boiling does not occur at any temperature, and it doesn’t require "very high" temperature — only the specific boiling point.
• Option (d) is incorrect because boiling is a liquid-gas change, not a solid-liquid change.

The boiling point is the temperature at which a liquid transforms into a gas throughout its entirety. Key points include:

• The boiling point occurs when the liquid's particles gain sufficient energy to change into vapour.
• For water, the boiling point is 373 K (or 100°C).
• This temperature is measured at standard atmospheric pressure.
• Boiling is a bulk phenomenon, meaning it affects the entire liquid.

In summary, the boiling point is crucial for understanding how substances transition from liquid to gas.

The latent heat of vaporization is the amount of heat energy needed to convert a liquid into a gas without changing its temperature. Here are some key points:

• This process occurs at the boiling point of the liquid.
• During vaporization, heat energy is absorbed, which allows particles to break free from each other.
• The term "latent" means hidden, as this heat does not raise the temperature.
• For water, the latent heat of vaporization is significant, as it requires a considerable amount of energy to change from liquid to gas.

In ice, hydrogen bonds hold water molecules in a rigid, open hexagonal lattice, spacing them farther apart than in liquid water, where molecules are closer together due to random movement. This results in ice having a lower density (0.92 g/cm³) than water (1 g/cm³), causing it to float. 

In solids, particles are closely packed in a fixed arrangement. This structure gives solids their definite shape and volume. Key characteristics include:

• Particles are tightly packed, making solids rigid.
• They maintain their shape unless a significant force is applied.
• Examples include items like wood, metal, and glass.

When subjected to force, solids may break, but their shape remains unchanged under normal conditions. This rigidity is a defining feature of the solid state of matter.

When the temperature of a solid increases:

• The kinetic energy of its particles rises.
• Particles begin to vibrate more quickly.
• This increased vibration can lead to a phase change, such as melting.
• As the solid continues to heat, particles may overcome the forces holding them in place, transitioning into a liquid state.

In summary, heating a solid causes its particles to move faster, which can eventually result in melting.

Water can exist in all three states:

• Solid: Ice
• Liquid: Water
• Gas: Steam

This transformation depends on temperature and pressure.

During these changes:

• In the solid state, particles are tightly packed.
• In the liquid state, particles are close but can move freely.
• In the gas state, particles are far apart and move rapidly.

Understanding these states helps explain various natural phenomena.