The number of moles in a substance indicates the amount of the substance that contains the same number of particles as 12 g of the Carbon-12 isotope [or equivalent to 6.02 × 10²³] (which is used as a standard in the world of moles).
Now,
if 6.02 × 10²³ atoms are found in 1 mole of mecury
then let 1.20 × 10²² atoms are found in x
⇒ x = (1.20 × 10²²) ÷ (6.02 × 10²³)
= 0.0199 moles
Now, mass = moles × molar mass
∴ mass of Hg = 0.0199 mol × 201 g/mol
= 4.001 g
∴ The mass in grams of a sample of 1.20 x 10²² atoms of mercury is ~ 4 g
