2 Answers

First figure out how many moles of hydrogen atoms you are looking for. Divide the number of atoms by Avogadro’s number (6.022 x 10^23) to get that.
4.95 x 10^24 atoms/6.022 x 10^23 = 8.22 moles of hydrogen atoms
For each mole of C3H8, you have 8 moles of hydrogen atoms, so divide the number of moles hydrogen by 8.
8.22 moles hydrogen x (1 mole C3H8/8 mole hydrogen)= 1.03 moles C3H8.

First off, Avogadro’s number states that one mole of any substance contains 6.02×10^23 particles(atoms, molecules, compounds, etc…)
So, we need to convert atoms to moles, right?
Conversion Factor:
4.95×10^24 atoms x (1 mole / 6.02×10^23 atoms)= 8.22259136 moles (because the atoms cancel each other out)=8.22 moles (we can only have 3 significant digits.)
Hope this helps!