Oxygen in air is a gas used by all the human beings and animals to breathe. About one-fifth (1/5) of the air is oxygen. That means there is about 21% of the oxygen in air.
Green plants release (give out) oxygen as a waste product in sunlight when they produce their food.
Reason: When oxygen is released, it will enter the test tube and the water will go down.
Green plants give out oxygen in sunlight.
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