The percentage of oxygen in room air is approximately:

Appeared in: NORCET 1 - 2020

Explanation

Room air is a mechanical mixture of gases, not a single element.
The normal composition of the air we breathe is approximately 78% nitrogen, 21% oxygen, and 1% other gases (including about 0.03-0.04% carbon dioxide).
This natural concentration of 21% oxygen is referred to as the Fraction of Inspired Oxygen (FiO₂) for a person breathing normally without assistance.

Option A: A 50% oxygen concentration is significantly higher than that found in room air and is considered a high-flow therapeutic dose.
Option B: 100% oxygen is a pure concentration that does not occur naturally in the atmosphere.
Option D: 90% is a very high concentration of oxygen not found in room air.

Visual 1: Pie Chart - A pie chart illustrating the composition of Earth's atmosphere, clearly showing Nitrogen (78%), Oxygen (21%), and Other Gases (1%). This provides a quick visual reference for the relative abundance of each gas.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Composition of atmospheric air as background academic context rather than a clinical decision trigger.
Understanding that room air is 21% oxygen is a fundamental concept for nurses to correctly administer supplemental oxygen and interpret a patient's response.
This knowledge provides the baseline for assessing a patient's oxygen saturation (SpO2). A healthy individual should have an SpO2 of 95-100% while breathing 21% oxygen (room air).
What if? If a patient's SpO2 drops to 90% on room air, the nurse recognizes the patient is hypoxic and anticipates the need for supplemental oxygen to increase the fraction of inspired oxygen (FiO2) above 21%.

How to Approach the Question

This is a factual recall question that tests foundational knowledge in respiratory physiology.
Identify the key components of the question: 'percentage of oxygen' and 'room air'.
Recall the standard composition of the air we breathe from your studies.
The atmosphere is primarily nitrogen (78%) and oxygen (21%).
Compare this recalled fact (21%) with the options provided.
Eliminate the other options (50%, 90%, 100%) by recognizing them as therapeutic concentrations of oxygen used in medical settings, not the natural composition of ambient air.

Concept Tested & Keywords

Qhrh-1pEiTBNuEFJz4TFQW

Practise the full NORCET 1 - 2020

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