States of Matter: Gas MCQs Quiz | Class 9

Test your understanding of Class IX Science, Unit I: Matter – Its Nature and Behaviour. This quiz covers the Gaseous state, including properties like lack of fixed shape and volume, high compressibility, and comparative density. Complete the 10 questions below and click Submit to check your score and download the PDF answer sheet.

Overview of the Gaseous State

In Class 9 Science, Unit I (Matter – Its Nature and Behaviour), the gaseous state is characterized by particles that are far apart and move randomly at high speeds. Unlike solids and liquids, gases have neither a fixed shape nor a fixed volume. They completely fill the vessel in which they are kept.

Key Properties of Gases

  • No Fixed Shape or Volume: Gases take the shape of the container and expand to fill the entire available volume.
  • High Compressibility: Because there is a lot of empty space between particles, gases can be compressed easily. This property is utilized in LPG (Liquefied Petroleum Gas) cylinders and CNG (Compressed Natural Gas) tanks.
  • Low Density: Compared to solids and liquids, gases have very low density because their mass is distributed over a much larger volume.
  • Pressure: Gas particles collide with each other and the walls of the container. The force exerted by gas particles per unit area on the walls of the container is defined as gas pressure.
  • Diffusion: Gases diffuse very rapidly into other gases due to the high speed of particles and large intermolecular spaces.

Comparison of States

Property Solid Liquid Gas
Shape Fixed Not fixed Not fixed
Volume Fixed Fixed Not fixed
Compressibility Negligible Low High
Particle Motion Vibrate in place Slide past each other Move freely and quickly

Quick Revision Points

  • Intermolecular Force: Weakest in gases, strongest in solids.
  • Intermolecular Space: Largest in gases, smallest in solids.
  • Kinetic Energy: Particles in a gas possess the highest kinetic energy among the three states.
  • Examples: Oxygen, Nitrogen, Carbon Dioxide, Helium, Steam.

Extra Practice Questions

  1. Why do gases exert pressure on the walls of a container?
  2. Explain why a gas fills a vessel completely.
  3. Why are gases highly compressible compared to liquids?
  4. What happens to the kinetic energy of gas particles when temperature increases?
  5. Define the term ‘diffusion’ with respect to gases.