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.

specific gravity is the density of a substance divided by the density of water. since (at standard temperature and pressure) water has a density of 1 gram/cm3, and since all of the units cancel, specific gravity is usually very close to the same value as density

so "c" is the answer

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the electrical  conductivity  of asolution  of an electrolyte is measured by determining the resistance of thesolution  between two flat or cylindrical electrodes separated by a fixed distance.