Final answer:
The proportion of oxygen in the air and the consequences of Earth's atmosphere disappearing are discussed.
Explanation:
The proportion of oxygen in the air is approximately 21%. Oxygen is considered an active gas because it readily reacts with other elements and compounds due to its high reactivity.
If Earth's atmosphere were to disappear, all living organisms depending on oxygen in the atmosphere would perish, leading to the extinction of almost all life forms on Earth.
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