Ambient air contains what percentage of oxygen by volume under standard conditions?

• A. Approximately 78%
• B. Approximately 21%
• C. Approximately 10%
• D. Approximately 50%

Answer: (B)

Verified step by step guidance

1. Understand that the problem asks for the percentage of oxygen in ambient air by volume under standard conditions, which refers to the typical composition of Earth's atmosphere at sea level and room temperature.
2. Recall that dry ambient air is primarily composed of nitrogen (N\_2), oxygen (O\_2), argon (Ar), carbon dioxide (CO\_2), and trace gases, with nitrogen and oxygen being the major components.
3. Remember the approximate volume percentages of the major gases: nitrogen is about 78%, oxygen is about 21%, and argon is about 1%, with other gases making up the remainder.
4. Identify that the percentage of oxygen by volume in ambient air is therefore approximately 21%, which is a well-established value in atmospheric chemistry.
5. Conclude that among the given options, the correct answer is 'Approximately 21%' because it matches the known composition of oxygen in ambient air.