Which is a pure substance? a. air b. nitrogen c. apple juice d. tap water

Explanation:

Because nitrogen is an element, that's is not combined with nothing. The air has molecules of other elements besides oxygen. Apple juice is a mixture a hydrogen, oxygen, and other elements. And tap water, even if is ''purified'' that's a lie, because pure water is not apt to human consumption.

- decrease the number of plants and animals living in the water.

the answer would be a