The atmosphere of the planet Venus is mainly composed of which gas?

Introduction / Context:
Understanding the composition of planetary atmospheres is an important part of astronomy and planetary science. Venus, often called Earths twin in size, has an atmosphere that is extremely different from that of Earth. This question checks whether you know which gas dominates the dense, hot atmosphere of Venus and creates its extreme greenhouse effect.

Given Data / Assumptions:

• The question refers to the main or dominant component of the Venusian atmosphere.

• Options list common gases: ammonia, carbon dioxide, helium, and hydrogen.

• Venus is known for very high surface temperatures and a strong greenhouse effect.

• Only one gas in the list matches the standard description of Venus atmosphere in textbooks.

Concept / Approach:
Planetary atmospheres can be compared by remembering which gas is most abundant. Earth atmosphere is dominated by nitrogen and oxygen, Mars has a thin atmosphere rich in carbon dioxide, and Venus has an extremely dense atmosphere that is also mainly carbon dioxide. This high concentration of carbon dioxide traps heat and leads to surface temperatures that are hotter than on Mercury, even though Mercury is closer to the Sun.

Step-by-Step Solution:
Step 1: Recall that Venus has a dense atmosphere that produces a very strong greenhouse effect. Step 2: Remember that carbon dioxide is a major greenhouse gas and is known to dominate the atmospheres of both Venus and Mars. Step 3: Recognise that ammonia is more commonly associated with outer planet atmospheres and is not the chief component of Venus air. Step 4: Note that helium and hydrogen dominate the atmospheres of gas giants like Jupiter and Saturn, not rocky planets like Venus. Step 5: Conclude that carbon dioxide is the correct answer, because it is the main constituent of the Venus atmosphere.

Verification / Alternative check:
Astronomy references describe Venus atmosphere as composed of more than ninety percent carbon dioxide, with small amounts of nitrogen and traces of other gases, along with clouds of sulfuric acid. The surface pressure is extremely high compared to Earth. These details are repeated in school level science books, encyclopedias, and planetary data tables, all of which confirm that carbon dioxide is the dominant gas.

Why Other Options Are Wrong:

• Ammonia does not form the main component of Venus atmosphere and is usually mentioned in relation to outer planet clouds.

• Helium is a light gas that is important in Jupiter and Saturn but is not the primary gas on Venus.

• Hydrogen is also dominant in gas giants but not in the thick, hot, rocky planet atmosphere of Venus.

Common Pitfalls:
Students sometimes memorise that Venus is very hot but forget the reason, or they confuse details of different planets. A useful strategy is to remember a quick association: Venus and Mars both have atmospheres dominated by carbon dioxide, whereas Jupiter and Saturn are dominated by hydrogen and helium. Keeping this pattern in mind helps avoid mixing up gases across planets.

Final Answer:
The atmosphere of Venus is mainly composed of Carbon dioxide.