Oxygen
Oxygen is a chemical element essential for breathing and combustion, making up about a fifth of the air.
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Deepika Nair
First written 1 Jun 2025
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Oxygen is a chemical element and a gas that makes up about 21 percent of the Earth's atmosphere. It is essential for most life.
Importance
Humans and animals breathe in oxygen to release energy from food. Oxygen is also needed for burning (combustion). Plants release oxygen during photosynthesis.
Properties
At normal conditions oxygen is a colourless, odourless gas. It combines with many other elements to form compounds, including water.
Frequently asked questions
Why is oxygen important?
Living things need it to breathe and release energy.
How much of the air is oxygen?
About 21 percent.