Na is 6.02 x 1023 atoms or molecules that you would call one mole.
If you have 0.1 mole (n=0.1) then you would have 6.02 x 1022 atoms or molecules.
If you have 6.02 x 1021 atoms then you would have 0.01 mole
If the mass number is 12 for carbon , then one mole of carbon is 12 g , then 0.1 mole would be 1.2 g . The mass of one atom would be 12g/6.02x1023. The mass of N atoms = N multiply 12 g/6.02x1023.
You can also use this: mass of one atom of carbon as 12u where u =1.66x10-27kg. How many carbon atoms are there in 1 kg of carbon? N = 1kg divide by 12u.
Two formulas for ideal gas equation:
pV = nRT or pV = NkT
