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Oxygen is the second most abundant gas, at about 20 percent, followed by argon at about 1 percent.
Oxygen is the second most abundant gas, at about 20 percent, followed by argon at about 1 percent.
Oxygen is the second most abundant gas, at about 20 percent, followed by argon at about 1 percent.
Oxygen is the second most abundant gas, at about 20 percent, followed by argon at about 1 percent.
1. Composing about 78 percent of the air at sea level, what is the most common gas in the Earth's atmosphere?
William & Mary professor Elizabeth Harbron displays vials with merocyanine and rhodamine dye in her lab in Williamsburg, Va. (Steve Helber/AP)
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