Question

The general atmospheric composition of gases in the decreasing order is ______.

• A. N2 > O2 > CO > CO2 > NH3
• B. N2 > O2 > CO2 > CO > NH3
• C. N2 > CO2 > O2 > NH3 > CO
• D. N2 > CO2 > NH3 > CO > O2

Hint:

Recall approximate atmospheric concentrations: nitrogen about 78%, oxygen about 21%, carbon dioxide about 0.04%, with carbon monoxide and ammonia as much smaller trace gases.

Answer 1

The Correct Option is B

This question tests recall of the typical volumetric composition of clean, dry atmospheric air, ranked from the most abundant to the least abundant of the listed gases.
Step 1: List the approximate abundance of each gas. Nitrogen makes up about 78 percent of the atmosphere by volume, oxygen makes up about 21 percent, carbon dioxide is present at trace levels of roughly 0.04 percent (around 400 ppm), carbon monoxide is a much smaller trace gas typically at sub-ppm to low ppm background levels, and ammonia occurs at even lower trace concentrations than carbon monoxide in the general atmosphere.
Step 2: Arrange in decreasing order. Ordering these five gases from highest to lowest concentration gives nitrogen first, followed by oxygen, then carbon dioxide, then carbon monoxide, and finally ammonia as the least abundant.
Step 3: Compare with the given options. This order, \(N_2 > O_2 > CO_2 > CO > NH_3\), matches option (B) exactly. Option (A) incorrectly places carbon monoxide above carbon dioxide, and options (C) and (D) incorrectly place carbon dioxide above oxygen, which is not the case for the general atmosphere.
Step 4: Conclude. The correct decreasing order of general atmospheric composition is nitrogen, oxygen, carbon dioxide, carbon monoxide, ammonia, which is option (B).