The chemical formula of propane is C3H8. Which number correctly uses scientific notation to represent the number of atoms in 2.00 moles of propane?

Avogadro's number represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. This number can be used to convert the number of atoms or molecules into number of moles. We do as follows:

2.00 mol C3H8 (6.022 x 10^23 atoms / mole) = 1.204x10^24 atoms C3H8