Question

Which of the following best defines one mole of a substance?

Answer 1

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.

Answer:

Amount of substance present in Avogadro's number of particles of the substance