A closed container has 7.05 ⋅ 1023 atoms of a gas. Each atom of the gas weighs 1.67 ⋅ 10-24 grams. Which of the following shows and explains the approximate total mass, in grams, of all the atoms of the gas in the container?

This can easily be solved using dimensional analysis - find a way to cancel out units. Since each atom weighs 1.67 x10^-24 grams, it could be written as: (1.67x10^-24 grams/atom)

Therefore

Total mass in grams of all atoms = (7.05 x 10^ 23 atoms) (1.67x10^-24 grams/atom) = 1.1774 grams