In the air that we breathe, which gas is the third most abundant component after nitrogen and oxygen?

Introduction / Context:
This general science question is about the composition of the Earth atmosphere. It asks which gas ranks third in abundance after the two main components, nitrogen and oxygen, in dry air at sea level.

Given Data / Assumptions:

• We are considering dry, unpolluted air at ground level.
• Nitrogen and oxygen are known to be the first and second most abundant gases.
• The options include argon, neon, carbon dioxide, hydrogen and ozone.
• We use approximate percentage compositions commonly quoted in textbooks.

Concept / Approach:
Dry air is mainly composed of nitrogen (about 78 percent) and oxygen (about 21 percent). The third most abundant gas by volume is argon, an inert noble gas, present at about 0.93 percent. Carbon dioxide accounts for only about 0.04 percent, and other gases like neon, hydrogen and ozone are present in much smaller trace amounts. Therefore, among the options, argon clearly ranks third in abundance.

Step-by-Step Solution:
1) Recall the approximate composition of dry air: nitrogen around 78 percent, oxygen around 21 percent.2) Together, nitrogen and oxygen make up roughly 99 percent of the atmosphere.3) The next largest fraction is argon, at about 0.93 percent by volume.4) Carbon dioxide is around 0.04 percent on average, much less than argon.5) Neon, hydrogen and ozone occur in even smaller trace amounts, so they cannot be the third most abundant gas.

Verification / Alternative check:
Standard environmental science and chemistry references list dry air composition as approximately 78 percent nitrogen, 21 percent oxygen, 0.93 percent argon and 0.04 percent carbon dioxide, with all other gases together making up less than 0.1 percent. This clearly confirms that argon is the third most abundant gas after nitrogen and oxygen under normal conditions.

Why Other Options Are Wrong:
Neon: Present only in tiny trace amounts, far below one percent, so it is not the third most abundant gas.
Carbon dioxide: Despite its importance for climate and photosynthesis, it makes up only about 0.04 percent of air, less than argon.
Hydrogen: Exists in very small trace concentrations in the atmosphere and is not a major component of air.
Ozone: Mostly concentrated in the upper atmosphere and present in extremely low concentrations near the surface, not significant in total volume.

Common Pitfalls:
Students sometimes choose carbon dioxide because it is frequently mentioned in discussions about global warming and the greenhouse effect. However, importance for climate does not mean abundance by volume. Always distinguish between relative concentration and environmental impact. Remember the simple order for air composition questions: nitrogen first, oxygen second and argon third.

Final Answer:
The third most abundant gas in the air we breathe, after nitrogen and oxygen, is argon.