How many atoms are there in 3.4moles if helium, show the calculation

Answer: 20.4752789138x x 10^23 atoms

To count how many atoms in moles you need to know Avogadro's number. Avogadro's number dictate that for every mole there is 6.022140857 * 10^23 molecule/atoms.

Then 3.4 moles of helium will be 3.4x 6.022140857 x 10^23 atoms = 20.4752789138x x 10^23 atoms