1 mole = 6.022x10²³ of anything. The number 6.022x10²³ is known as Avogadro's number. Avogadro's number is not a mass, it is just a unit of measure. Other units of measure include: 1 pair (2), 1 dozen (12), a baker's dozen (13), et. al. 1 mole is similar in that it simply represents a certain number of things; specifically, Avogadro's number of things.
Since we know 1 mole is not a mass, the first two options can be eliminated. On observing the third option, it cannot be correct because, as we said, 1 mole is equal to Avogadro's number—not an atom of a given substance.
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Answer:</h3>
Amount of substance present in Avogadro's number of particles of the substance
