Approximately how much of the air we breathe is composed of nitrogen and oxygen combined?

• A. About 50%
• B. About 99%
• C. About 98%
• D. About 78%

Answer: (C)

Verified step by step guidance

1. Recall the approximate composition of Earth's atmosphere by volume: nitrogen (N\_2) makes up about 78%, oxygen (O\_2) about 21%, and the remaining 1% consists of other gases such as argon, carbon dioxide, and trace gases.
2. To find the combined percentage of nitrogen and oxygen, add their individual percentages together: 78% (N\_2) + 21% (O\_2).
3. Express this sum as a percentage to understand how much of the air is composed of these two gases combined.
4. Compare the calculated combined percentage to the given answer choices to identify the closest value.
5. Conclude that since nitrogen and oxygen together make up approximately 99% of air, the answer closest to this value is the correct one.