In the composition of the Earth atmosphere, which one of the following gases is the most abundant by volume?

Introduction / Context:
This general knowledge question tests your basic understanding of the composition of air. While we often focus on oxygen because it is essential for respiration, nitrogen actually makes up the largest fraction of the atmosphere by volume. Knowing the major gases and their approximate percentages is important for both chemistry and geography topics.

Given Data / Assumptions:

• The options list argon, nitrogen, oxygen, krypton and carbon dioxide.
• The question asks for the most abundant gas in the atmosphere by volume.
• We are referring to the lower atmosphere near the Earth surface and to average dry air.

Concept / Approach:
Dry air close to the Earth surface is composed mainly of nitrogen and oxygen, with smaller amounts of argon, carbon dioxide and trace gases. Standard composition data state that nitrogen is about 78 percent by volume and oxygen about 21 percent. Argon is less than 1 percent, carbon dioxide is a small fraction of a percent, and krypton is present in trace amounts. Therefore, among the listed gases, nitrogen is clearly the most abundant component of the atmosphere.

Step-by-Step Solution:

Verification / Alternative check:
Every basic science textbook and reference chart of air composition begins with nitrogen as the major component. Classroom posters and diagrams often show a large sector representing nitrogen in pie charts of the atmosphere. Meteorology and environmental science resources also highlight the dominance of nitrogen, followed by oxygen. Checking any such reliable source confirms that nitrogen is the correct answer to this question, with oxygen a clear second and other gases far behind.

Why Other Options Are Wrong:

• Argon: It is a noble gas present at less than 1 percent by volume, so it is not the most abundant gas.
• Oxygen: Oxygen is the second most abundant gas at about 21 percent, but nitrogen still exceeds it.
• Krypton: This is a trace noble gas present in very tiny amounts and cannot be the major component.
• Carbon dioxide: Even though it is important for climate and photosynthesis, its volume percentage is small compared with nitrogen and oxygen.

Common Pitfalls:
Because oxygen is so important for life, some learners mistakenly think it must be the main component of air. Similarly, climate news emphasises carbon dioxide, which can cause people to overestimate its quantity. Remember that importance for life or climate is not the same as abundance. For exam questions, always recall that nitrogen is the most abundant gas in air by volume, followed by oxygen, with other gases present in much smaller proportions.

Final Answer:
The most abundant gas in the atmosphere of Earth is Nitrogen.