Q. What is the approximate percentage of oxygen in Earth's atmosphere?
Answer: 21
Notes: Oxygen is the second important constituent(first being nitrogen) of Earth's atmosphere. Percentage of oxygen present in air is approximately 21%(20.95%).

This question is part of 40000+ General Studies MCQ Series Course on GKToday Android app. Question Number: 33 in General Studies Mock Test - 33 in above course in App.