How many nitrogens are in one molecule of N2O?
How many nitrogens are in six molecules of N2O?
So, how many nitrogens are in 2.05 x 1022 molecules of N2O?
If I take three apples and remove one how many do I have? Two, because I have removed one third of the apples, and have two thirds of three left, right?
You know how many N atoms are in 1.5 of nitrous oxide, so if you take away 0.5 g, to leave you with 1 g of nitrous oxide, you have removed one third of the nitrous oxide (and with that one third of the nitrogen), so how many atoms do you have left?