Aluminum Al2713 has an atomic molar mass of 27 grams per mole.
Al has 13 protons (hence number 13) and it most common isotope 14 neutrons for a total mass of 27 amu. ( The 13 electrons add no measurable mass to the atom)
Take the grams and divide by the molar mass
= 2 moles
The atmosphere contains the air we breathe
4 because it's electron configuration is 1s2 2s2 2p2 and to have a full outer valence shell you need 2p6 so you only need 4 more electrons to get to 2p6.
Llowing certain substances to pass through it but not others, especially allowing the passage of a solvent but not of certain solutes.