Answer:
amount of He = (7.91 × 10^22) ÷ (6.02 × 10^23) = 0.131mol (3sf)
Explanation:
you make use of the mole concept formula
amount(mol) = number of particles ÷ 6.02 × 10^23
(6.02 × 10^23 is the avogadro constant, which is an extremely important number in this formula for mole concept)
