Which gas is most abundant in the Earth's atmosphere?

Appeared in: NORCET 8 Prelims-2025

Explanation

Nitrogen (N₂) is the most plentiful gas in the Earth's atmosphere, constituting about 78% of the total volume.
This high concentration makes it the primary component of the air we breathe, far exceeding all other gases.
It serves as a crucial diluent for oxygen, which helps to control combustion and makes the atmosphere more stable for life.

Option A: Oxygen is the second most abundant gas in the atmosphere, making up about 21%.
Option C: Carbon dioxide (CO₂) is a trace gas, accounting for only about 0.04% of the atmosphere.
Option D: This option is incorrect because the correct answer, Nitrogen, is provided as one of the choices.

Visual 1: Pie Chart - A pie chart visually representing the percentage composition of gases in the Earth's atmosphere. The largest slice (78%) should be labeled 'Nitrogen,' followed by 'Oxygen' (21%), 'Argon' (0.9%), and a very small slice for 'Other Gases' (0.1%).

Clinical Relevance

Nursing practice connection: Knowing Composition of Earth's Atmosphere helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding that room air is 21% oxygen is fundamental in respiratory therapy. All supplemental oxygen administration is based on increasing the fraction of inspired oxygen (FiO₂) above this baseline.
While atmospheric nitrogen is mostly inert to the body, compressed nitrogen is the basis of the decompression sickness ('the bends') seen in divers, a critical emergency condition.
Liquid nitrogen is widely used in clinical settings for cryosurgery (to destroy abnormal tissue) and cryopreservation (to store biological samples at very low temperatures).

How to Approach the Question

First, identify the key directive in the question: 'most abundant'. This asks for the gas with the highest concentration.
This is a factual recall question from general science. Access your knowledge about the composition of the Earth's atmosphere.
Recall the approximate percentages of the main gases: Nitrogen is about 78%, and Oxygen is about 21%.
Compare these values. 78% is significantly higher than 21%.
Therefore, Nitrogen is the most abundant gas.
Select the option that matches this fact.

Concept Tested & Keywords

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Practise the full NORCET 8 Prelims-2025

Attempt every question from this paper in a timed mock, then review the full solution for each one.