Important Exam Questions: Matter in Our Surroundings | Science Class 9 PDF Download

Answer: Matter is anything that occupies space and has mass. Examples: Water (liquid), Air (gas).

Answer: b) Anything that occupies space and has mass

Answer: When salt is dissolved in water, the salt particles occupy the empty spaces (voids) between the water molecules. This does not increase the volume of the solution, so the water level remains unchanged.

Answer:Latent heat is the heat energy required to change the state of a substance without changing its temperature.

• Latent heat of fusion: Heat energy needed to convert 1 kg of a solid into a liquid at its melting point (e.g., 3.34 × 10⁵ J/kg for ice).
• Latent heat of vaporization: Heat energy needed to convert 1 kg of a liquid into a gas at its boiling point (e.g., 22.5 × 10⁵ J/kg for water).

Answer: On a windy day, the wind carries away water vapor particles from the surface of the clothes, reducing humidity around them. This increases the rate of evaporation, causing clothes to dry faster.

Answer: Sublimation is the process where a solid changes directly into a gas without passing through the liquid state. Examples: Camphor, Ammonium chloride.

Answer: b) 3.34 × 10⁵ J/kg

Answer:The rate of evaporation is affected by:

Nature of liquid: Liquids with weaker intermolecular forces (e.g., acetone) evaporate faster than those with stronger forces (e.g., water).

Surface area: Larger surface areas increase evaporation (e.g., clothes dry faster when spread out).

Temperature: Higher temperatures increase evaporation (e.g., clothes dry faster in summer).

Humidity: Lower humidity increases evaporation (e.g., clothes dry slower in rainy seasons due to high humidity).

Wind speed: Higher wind speed removes water vapor, increasing evaporation (e.g., clothes dry faster on windy days).

Answer: Both assertion and reason are true, and the reason is the correct explanation of the assertion.

Answer: Process: Sublimation is the direct conversion of a solid to a gas without passing through the liquid state. When heated, ammonium chloride turns into vapor, which cools and deposits as a solid (sublimate).
Diagram: 

Answer:
a) The experiment demonstrates that matter is made up of tiny particles (molecules).
b) The color intensity decreases because dilution reduces the number of potassium permanganate particles in the solution, spreading them over a larger volume of water.
c) It shows that matter consists of extremely small particles, as even a few crystals contain millions of molecules that spread uniformly in water, causing a visible color change.

Answer:

Solid: Tightly packed particles in a regular pattern, minimal movement (vibration only).

Liquid: Loosely packed particles, able to move within a fixed volume, taking the container’s shape.

Gas: Widely spaced particles, moving freely, filling the entire container.

Answer: c) It increases