Olympiad Test: Matter - 1 - Class 5 MCQ

In solids, the molecules are tightly packed together due to strong intermolecular forces, resulting in minimal space between them. This arrangement gives solids their fixed shape and volume. In contrast:

• In liquids, molecules are less tightly packed, allowing for some movement.
• In gases, molecules are widely spaced and move freely.

Therefore, the least intermolecular space is found in solids.

The freezing point of water is 0°C, while the boiling point is 100°C at standard atmospheric pressure. These temperatures represent the points at which water transitions from:

• Liquid to Solid (freezing)
• Liquid to Gas (boiling)

Thus, the correct answer is Option B (100°C).

When a substance changes from a solid to a liquid, it is undergoing the melting process. This occurs at the melting point, where the substance:

• Absorbs heat
• Molecules gain energy
• Transitions into the liquid state

During melting, the solid structure breaks down, allowing the material to flow as a liquid.

Molecules of gases are characterised by their unique behaviour:

• Widely spaced: Gas molecules are far apart from one another.
• High energy: They possess significant energy, enabling movement.
• Free movement: Gas molecules can move freely in all directions.
• Expansion: Gases expand to fill any available space.

This behaviour contrasts with that of solids and liquids, which maintain a fixed shape and volume.

When heat is supplied to molecules, their kinetic energy increases. The added heat causes the molecules to move faster, resulting in:

• Increased motion
• Higher energy levels
• Expansion of substances
• Possible change of state

This explains why substances can expand or change their state when they absorb heat.

All three, steam, oxygen, and carbon dioxide, can be compressed.

• Steam is a gas and, like any gas, can be compressed by reducing the volume and increasing the pressure.
• Oxygen is a gas and can also be compressed under pressure.
• Carbon dioxide is a gas and can be compressed into a liquid or solid form under high pressure.

Therefore, the correct answer is Option D (P, Q and R).

• A: Solids can freeze - Solids are already in a frozen state, so this statement is not about freezing but rather about maintaining their solid form.
• B: Liquids can freeze - This is the correct statement because liquids freeze when the temperature drops below their freezing point, turning into solids (like water freezing into ice).
• C: Gases can freeze - Gases can indeed turn into solids under extreme conditions, but freezing is generally associated with the liquid-to-solid phase change.
• D: All of the above - This option includes gases, which do not typically freeze in the common sense of the term.

Therefore, Option B is the correct choice, as liquids can freeze when cooled below their freezing

Both water vapor and steam are classified as gases. They share the following characteristics:

• They have no definite shape.
• They have no definite volume.
• They expand to fill any container.

While steam is the gaseous form of water produced at boiling point, water vapor refers to water in its gaseous state below boiling. In essence, both exhibit the typical properties of gases.

Molecules are the components of solids, matter, and solutions. Here's why:

• Solids: In solids, molecules are tightly packed together in a fixed structure.
• Matter: Matter, in general, is anything that has mass and takes up space, and it is composed of molecules.
• Solutions: In solutions, molecules of the solute are dispersed within the solvent.

Therefore, molecules are fundamental components of all these categories.

The ability of liquids to flow is due to the fact that their particles are not tightly packed like in solids. The particles have enough space between them to move or slide past each other, allowing the liquid to flow and take the shape of its container. This is a key characteristic of liquids.