A mole is the amount of a substance that contains as many particles as the number of atoms in 12 grams of what isotope?

A) Boron-12

B) Carbon-12

C) Calcium-39

D) Aluminum-26

To determine the element, we must take reference to the periodic table to confirm each element and its equivalent atomic weight. The given is 12 grams of the isotope per mole of it. Hence, we must find out the element in the periodic table which has an atomic weight of 12. The element is carbon, hence answer is B.