Natural Science CLEP Prep Practice Exam

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Prepare for the CLEP Natural Science Exam with our comprehensive study materials and practice questions. Test your knowledge and ace the exam by mastering key concepts.

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Which gas makes up 78% of the Earth's atmosphere?

Nitrogen
Oxygen
Carbon dioxide
Methane

The correct answer is: Nitrogen

Nitrogen makes up 78% of Earth's atmosphere. Oxygen only accounts for 21%, while carbon dioxide and methane make up very small amounts. Carbon dioxide composes about 0.04% of the atmosphere, and methane makes up even less at around 0.00017%. Therefore, neither carbon dioxide nor methane are correct options for the gas that makes up 78% of Earth's atmosphere. It is important to note that while oxygen is a crucial gas for life on Earth, it does not make up the majority of the atmosphere as only a small portion is necessary for sustaining life.