Which option correctly lists the major gases in Earth atmosphere and their approximate percentages by volume at sea level?

Introduction / Context:
This question evaluates your knowledge of the composition of the lower atmosphere of Earth. Knowing which gases are most abundant and their approximate percentages is fundamental for understanding weather, climate, respiration, and many environmental processes. It is a common topic in general science, geography, and competitive exams.

Given Data / Assumptions:

• The question refers to the major gases in the atmosphere near sea level in the lower layer, known as the troposphere.
• Trace gases like carbon dioxide have small but important percentages by volume.
• Approximate, rounded values are sufficient for exam purposes, not extremely precise decimal values.

Concept / Approach:
Dry air in the lower atmosphere is dominated by a few gases. Nitrogen is the most abundant gas, making up roughly 78 percent by volume. Oxygen is the second most abundant at about 21 percent. Argon, a noble gas, contributes about 0.93 percent. Carbon dioxide is a trace but very important greenhouse gas present at roughly 0.04 percent by volume in recent times. Variable amounts of water vapour are also present, but its percentage changes greatly from place to place and day to day, so it is usually not given a single fixed percentage in simple tables. The correct answer must reproduce these approximate values in the right order, while incorrect options will either swap gases or give unrealistic numbers.

Step-by-Step Solution:

Verification / Alternative check:
You can quickly verify these figures by checking a school geography or environmental science textbook table summarising the composition of dry air. Many educational charts show a pie diagram with approximately 78 percent nitrogen, 21 percent oxygen, just under 1 percent argon, and a very small slice for carbon dioxide and other trace gases. International meteorological and climate organizations use similar standard compositions as a reference for modelling and calculations. This independent confirmation supports option A as the accurate description.

Why Other Options Are Wrong:

Oxygen 50 percent, nitrogen 49 percent, carbon dioxide 1 percent is wrong because it reverses the dominance of nitrogen and oxygen and gives carbon dioxide a value that is far too high compared with measured atmospheric levels.

Nitrogen 60 percent, oxygen 30 percent, water vapour 10 percent is incorrect because it underestimates nitrogen and overestimates both oxygen and water vapour. The percentage of water vapour is highly variable and not fixed at 10 percent.

Oxygen 78 percent, nitrogen 21 percent, carbon dioxide 1 percent is wrong because it swaps oxygen and nitrogen and again exaggerates carbon dioxide, which is present at less than one tenth of one percent by volume.

Common Pitfalls:
Students often remember only that nitrogen and oxygen are the main gases but confuse which one is larger in percentage. Another frequent mistake is to guess that carbon dioxide is around 1 percent because it is famous in discussions of climate change, even though its actual concentration is much lower. Learners may also forget about argon, a noble gas, because it is chemically inert and rarely discussed in everyday contexts, yet it is the third most abundant gas. Carefully studying standard atmospheric composition tables prevents these errors.

Final Answer:
The correct description of the major atmospheric gases and their approximate percentages is Nitrogen 78 percent, oxygen 21 percent, argon 0.93 percent, carbon dioxide about 0.04 percent.