Question

You are given a sample containing 0.90 moles of a substance. How many atoms are in the sample if the substance is copper?

Answer 1

To find the atoms of a substance all you have to do is times the moles by avogadros number which is \[6.02 \times 10^{23}\].

So, as you already have the moles you wont have to do a lot of calculations.

No. of atoms = Moles of substance (0.9 mol) x Avogadro's number (6.02x10^23)

Do that and then you should get your answer :)