**Definition of a Planet**
A planet is a celestial body that orbits a star (like the Sun) and is massive enough to be rounded by its gravity but not massive enough to initiate thermonuclear fusion (as stars do). In our solar system, we recognize eight major planets, divided into two main categories: **terrestrial planets** and **gas giants**.

 **Solar System Planets:**
1. **Mercury**:
   - Smallest planet.
   - Closest to the Sun.
   - It has a rocky surface with extreme temperatures ranging from hot during the day to freezing cold at night.
   - No atmosphere, hence no weather.

2. **Venus**:
   - Similar in size and structure to Earth, often called Earth’s “sister planet.”
   - Thick, toxic atmosphere made up mostly of carbon dioxide with clouds of sulfuric acid.
   - Extremely high surface temperatures due to the greenhouse effect.

3. **Earth**:
   - Only planet known to support life.
   - 70% of the planet's surface is covered in water.
   - Atmosphere composed primarily of nitrogen and oxygen.

4. **Mars**:
   - Known as the "Red Planet" because of iron oxide (rust) on its surface.
   - Thin atmosphere made mostly of carbon dioxide.
   - Polar ice caps and the largest volcano in the solar system, Olympus Mons.

5. **Jupiter**:
   - Largest planet in the solar system.
   - A gas giant composed mostly of hydrogen and helium.
   - Known for its Great Red Spot, a massive storm that has been raging for centuries.
   - Has 79 known moons, including Ganymede, the largest moon in the solar system.

6. **Saturn**:
   - Known for its extensive ring system.
   - A gas giant like Jupiter, composed mostly of hydrogen and helium.
   - Has 83 known moons, including Titan, which has a thick atmosphere and rivers of liquid methane.

7. **Uranus**:
   - Ice giant with a pale blue color due to methane in its atmosphere.
   - Uniquely, it rotates on its side, which means it has extreme seasons.
   - Composed of water, ammonia, and methane ice, along with hydrogen and helium gases.

8. **Neptune**:
   - Ice giant similar to Uranus.
   - Has the strongest winds in the solar system.
   - Known for its deep blue color, also due to methane in its atmosphere.
   - Has 14 known moons, including Triton, which has geysers of nitrogen.

 **Important Concepts Related to Planets:**
1. **Orbit**: The path of a planet around the Sun, typically elliptical.
2. **Rotation**: The spinning of a planet on its axis. Earth rotates once every 24 hours, leading to day and night.
3. **Revolution**: The time it takes for a planet to complete one orbit around the Sun. Earth takes 365.25 days.
4. **Atmosphere**: A layer of gases surrounding a planet. Earth’s atmosphere is breathable for humans, while other planets have atmospheres composed of gases like carbon dioxide, methane, and hydrogen.

 **30 Multiple Choice Questions on Planets (With Answers)**

1. **Which is the smallest planet in our solar system?**  
   a) Mercury  
   b) Venus  
   c) Earth  
   d) Mars  
   **Answer:** a) Mercury

2. **Which planet is known as the "Red Planet"?**  
   a) Venus  
   b) Mars  
   c) Jupiter  
   d) Saturn  
   **Answer:** b) Mars

3. **Which planet has the most extensive ring system?**  
   a) Neptune  
   b) Saturn  
   c) Uranus  
   d) Jupiter  
   **Answer:** b) Saturn

4. **Which planet is the hottest in the solar system?**  
   a) Mercury  
   b) Venus  
   c) Mars  
   d) Earth  
   **Answer:** b) Venus

5. **Which planet is known for the Great Red Spot?**  
   a) Mars  
   b) Saturn  
   c) Jupiter  
   d) Neptune  
   **Answer:** c) Jupiter

6. **Which planet has a day longer than its year?**  
   a) Mercury  
   b) Venus  
   c) Earth  
   d) Mars  
   **Answer:** b) Venus

7. **Which planet has the largest moon in the solar system?**  
   a) Jupiter  
   b) Saturn  
   c) Uranus  
   d) Neptune  
   **Answer:** a) Jupiter (Ganymede)

8. **Which planet is tilted on its side?**  
   a) Jupiter  
   b) Saturn  
   c) Uranus  
   d) Neptune  
   **Answer:** c) Uranus

9. **Which planet has the fastest winds in the solar system?**  
   a) Jupiter  
   b) Mars  
   c) Saturn  
   d) Neptune  
   **Answer:** d) Neptune

10. **Which planet is closest to the Sun?**  
   a) Mercury  
   b) Venus  
   c) Earth  
   d) Mars  
   **Answer:** a) Mercury

11. **Which planet has water in all three forms (solid, liquid, gas)?**  
   a) Mercury  
   b) Venus  
   c) Earth  
   d) Mars  
   **Answer:** c) Earth

12. **What is the largest planet in the solar system?**  
   a) Earth  
   b) Mars  
   c) Jupiter  
   d) Saturn  
   **Answer:** c) Jupiter

13. **Which planet has the most moons?**  
   a) Saturn  
   b) Jupiter  
   c) Uranus  
   d) Neptune  
   **Answer:** b) Jupiter

14. **Which planet has the longest year?**  
   a) Neptune  
   b) Uranus  
   c) Saturn  
   d) Jupiter  
   **Answer:** a) Neptune

15. **Which planet has polar ice caps?**  
   a) Mercury  
   b) Venus  
   c) Mars  
   d) Saturn  
   **Answer:** c) Mars

16. **Which planet is known for its extreme seasons?**  
   a) Uranus  
   b) Neptune  
   c) Saturn  
   d) Jupiter  
   **Answer:** a) Uranus

17. **Which planet has the most active volcano in the solar system?**  
   a) Venus  
   b) Mars  
   c) Earth  
   d) Jupiter  
   **Answer:** d) Jupiter (Io, a moon)

18. **Which planet has a day lasting only about 10 hours?**  
   a) Mercury  
   b) Jupiter  
   c) Saturn  
   d) Uranus  
   **Answer:** b) Jupiter

19. **What planet is referred to as Earth’s twin?**  
   a) Mars  
   b) Venus  
   c) Neptune  
   d) Mercury  
   **Answer:** b) Venus

20. **Which planet has nitrogen geysers?**  
   a) Jupiter  
   b) Saturn  
   c) Uranus  
   d) Neptune  
   **Answer:** d) Neptune (Triton)

21. **Which planet takes 88 Earth days to orbit the Sun?**  
   a) Mercury  
   b) Venus  
   c) Earth  
   d) Mars  
   **Answer:** a) Mercury

22. **Which planet is known as the “Morning Star” and the “Evening Star”?**  
   a) Mercury  
   b) Venus  
   c) Mars  
   d) Jupiter  
   **Answer:** b) Venus

23. **What planet is home to the Olympus Mons volcano?**  
   a) Earth  
   b) Mars  
   c) Jupiter  
   d) Venus  
   **Answer:** b) Mars

24. **Which planet's atmosphere consists primarily of carbon dioxide?**  
   a) Venus  
   b) Mars  
   c) Earth  
   d) Jupiter  
   **Answer:** a) Venus

25. **Which planet is the farthest from the Sun?**  
   a) Neptune  
   b) Uranus  
   c) Saturn  
   d) Jupiter  
   **Answer:** a) Neptune

26. **Which planet is often called the “blue planet” due to its water bodies?**  
   a) Mars  
   b) Uranus  
   c) Earth  
   d) Neptune  
   **Answer:** c) Earth

27. **Which planet is known for having methane in its atmosphere giving it a blue color?**  
   a) Neptune  
   b) Uranus  
   c) Saturn  
   d) Jupiter  
   **Answer:** a) Neptune

28. **What is the primary gas in the atmosphere of Uranus and Neptune?**  
   a) Carbon Dioxide  
   b) Hydrogen  
   c) Methane  
   d) Nitrogen  
   **Answer:** c) Methane

29. **What planet has an orbit period of 165 Earth years?**  
   a) Uranus  
   b) Neptune  
   c) Saturn  
   d) Jupiter  
   **Answer:** b) Neptune

30. **Which planet's atmosphere contains a large amount of nitrogen and oxygen?**  
   a) Mars  
   b) Earth  
   c) Jupiter  
   d) Saturn  
   **Answer:** b) Earth

31. **Which planet has 83 moons, including Titan?**  
   a) Saturn