Canadian Entry To Practice (CETP) Practice Test

Disable ads (and more) with a membership for a one time $2.99 payment

Prepare for the Canadian Entry To Practice Test. Study with various question formats, including flashcards and multiple-choice questions, complete with hints and explanations. Ensure you're ready for your test!

Each practice test/flash card set has 50 randomly selected questions from a bank of over 500. You'll get a new set of questions each time!

Practice this question and more.

Approximately what percentage of air is oxygen?

The correct answer is: 20%

The percentage of oxygen in the Earth's atmosphere is approximately 20%. This proportion is significant for several reasons, including its role in supporting life through respiration for many organisms. The oxygen content is a stable component of the atmosphere and is essential for combustion processes, making it critical for various chemical reactions and biological functions. In the context of the other options, 10% would be insufficient for sustaining aerobic life, as most organisms rely on a higher concentration of oxygen for efficient energy production. Similarly, 30% and 40% are overestimates, as such high levels of oxygen could lead to toxicity in biological systems and also increase the risk of fire and combustion hazards. Thus, the accurate figure of around 20% reflects the balanced composition of the atmosphere necessary for life on Earth.