The chemical formula of ethane is C2H6 which means that every mole of ethane contains 2 moles of carbon atom and 6 moles of hydrogen atom.
a. (3 moles) x (2 moles C atom / 1 mole ethane) = 6 moles C atom
b. (3 moles) x (6 moles H atom / 1 mole ethane) = 18 moles H atom
c. (3 moles ethane) x (6.022 x 10^23 molecules / 1 mole) = 1.8 x 10^24 molecules.
