The mass number of Argon is 39.948 so it is 119.98/39.948=3.0034 moles of Argon in 119.98 g of Argon or approximately 3 moles of Argon is in 119.98 g this gas.
From the Periodic Table, Argon has an atomic weight of 39.948. One mole of any element is equal to its atomic weight in grams. So 1 mole of Ar = 39.948g of Ar. Using that equality, you do the...