Key Stage 3 (KS3) General Knowledge Practice Test 2026 - Free KS3 Practice Questions and Study Guide

The most abundant gas in the Earth's atmosphere is nitrogen. Approximately 78% of the atmosphere is composed of nitrogen, making it a crucial component for various biological and chemical processes. Nitrogen is an inert gas under normal conditions, meaning it does not easily react with other substances, which helps maintain a stable atmosphere.

While oxygen is essential for life and accounts for about 21% of the atmosphere, it is less abundant than nitrogen. Carbon dioxide, despite its importance in processes like photosynthesis and its role in climate change, makes up only about 0.04% of the atmosphere. Helium, on the other hand, is a much rarer gas in the atmosphere, found in trace amounts. Understanding the composition of the atmosphere is important for studying environmental science and the impacts of various gases on our planet.