Air we breathe has ___ % oxygen.

## The reasoning The atmosphere around us is a **mixture of gases**, not pure oxygen. By volume, air contains approximately: - **78% Nitrogen** (the most abundant) - **21% Oxygen** (what we need for respiration) - **1% other gases** (argon, carbon dioxide, trace gases) So the air you're breathing right now is roughly **one-fifth oxygen**. This 21% is perfectly balanced for life — enough to keep us alive, but not so much that everything catches fire easily! ## Why the wrong options tempt you **10%** — Too low! This might come from confusing oxygen with carbon dioxide (which is only about 0.04%). **50%** — This feels intuitive because "we need oxygen to survive," but half the air being oxygen would make combustion way too easy and dangerous. **75%** — This probably confuses oxygen with nitrogen, which actually makes up about 78% of air. ## Quick takeaway **Remember the "78-21-1 rule"**: Air is roughly 78% nitrogen, 21% oxygen, and 1% everything else — we breathe a nitrogen-rich mix, not pure oxygen!