Question

which percent of earth’s atmosphere does carbon dioxide gas make up? (1 point)
○ more than 99 percent
○ about 78 percent
○ less than 1 percent
○ about 21 percent

Explanation:

To determine the percentage of Earth's atmosphere that carbon dioxide (\(CO_2\)) makes up, we recall the composition of Earth's atmosphere. The major components are nitrogen (about 78%), oxygen (about 21%), and the remaining gases (including argon, carbon dioxide, water vapor, etc.) make up less than 1% of the atmosphere. Carbon dioxide is a trace gas in this remaining portion, so it makes up less than 1% of the atmosphere.

• "more than 99 percent" is incorrect because no single gas (except in extreme cases not applicable here) makes up that much, and nitrogen and oxygen are the main components.
• "about 78 percent" is the percentage of nitrogen, not \(CO_2\).
• "about 21 percent" is the percentage of oxygen, not \(CO_2\).
• "less than 1 percent" is correct as \(CO_2\) is a trace gas in the atmosphere.

Answer:

C. less than 1 percent (assuming the options are labeled A, B, C, D with A: more than 99 percent, B: about 78 percent, C: less than 1 percent, D: about 21 percent)