Which of the following lists the approximate concentration (by volume) of CO_2, N_2, and O_2 in dry air?

• A. CO_2: 21%, N_2: 78%, O_2: 0.04%
• B. CO_2: 21%, N_2: 0.04%, O_2: 78%
• C. CO_2: 0.04%, N_2: 78%, O_2: 21%
• D. CO_2: 78%, N_2: 21%, O_2: 0.04%

Answer: (C)

Verified step by step guidance

1. Understand that the problem asks for the approximate volume percentages of carbon dioxide (CO_2), nitrogen (N_2), and oxygen (O_2) in dry air, which is a common composition question in general chemistry.
2. Recall that dry air is primarily composed of nitrogen and oxygen, with nitrogen making up the largest portion, oxygen the second largest, and carbon dioxide a very small fraction.
3. Remember the typical approximate volume percentages of these gases in dry air: nitrogen (N_2) is about 78%, oxygen (O_2) is about 21%, and carbon dioxide (CO_2) is about 0.04%.
4. Compare the given options to these known approximate values to identify which list matches the typical composition of dry air.
5. Select the option where CO_2 is approximately 0.04%, N_2 is approximately 78%, and O_2 is approximately 21%, as this correctly represents the volume concentration of these gases in dry air.