Matter - Class 8 Physics ICSE Free MCQ Test with solutions

In solids, the kinetic energy of molecules primarily allows them to vibrate in place. This limited movement is due to the strong forces of attraction that hold the molecules tightly together.

The process where a solid changes directly into a gas is called sublimation. An example of sublimation occurs with dry ice (solid carbon dioxide), which transitions to gas without becoming a liquid first.

Gases do not have a fixed shape or volume. They expand to fill the container they are in, which is a key characteristic that distinguishes gases from solids and liquids.

As a liquid heats up, its molecules gain kinetic energy and begin to move more freely. This increased motion can eventually lead to the liquid boiling and turning into gas if enough heat is applied.

Latent heat refers to the heat absorbed or released by a substance during a change of state (like melting or boiling) without causing a temperature change. This concept is crucial for understanding phase transitions in matter.

The force of attraction between molecules in solids is very strong due to the close proximity of the molecules. This strong intermolecular force is what gives solids their definite shape and rigid structure, distinguishing them from liquids and gases.

A diatomic molecule is defined as a molecule consisting of two atoms. Common examples include oxygen (O₂) and hydrogen (H₂). This classification is important in understanding the composition of many gases in the atmosphere.

Matter is defined as anything that has mass and occupies space. This includes all forms of matter—solids, liquids, and gases.

The process of changing from a solid to a liquid is known as melting. This occurs when a solid is heated to its melting point, allowing its molecules to gain sufficient energy to overcome their fixed positions and move freely, thus forming a liquid.

When sweat evaporates, it absorbs heat from the skin, which cools the surface. This cooling effect is beneficial for regulating body temperature, especially in hot conditions.

In a gas state, molecules move randomly and are spaced far apart, allowing them to fill any container they occupy. This freedom of movement is a defining characteristic of gases, contrasting significantly with the behavior of molecules in solids and liquids.

The boiling point of a liquid increases with an increase in pressure. This is why pressure cookers can cook food faster; they create a higher pressure environment that raises the boiling point of water.

The melting point of ice at standard atmospheric pressure is 0°C. At this temperature, ice absorbs heat without changing temperature until it fully transitions into liquid water.

The process of a gas turning into a liquid is known as condensation. This occurs when gas molecules lose energy and come together to form a liquid, a process observed when water vapor in the air cools and forms droplets.

The presence of humidity decreases the rate of evaporation. In humid conditions, the air is already saturated with water vapor, which makes it more difficult for additional moisture to evaporate into the air. This is why clothes take longer to dry on humid days.