In order to find the number of atoms in 2.3 grams of Carbon, we need to find out how many moles we have, and we will be using the molar mass, 12g/mol, to find it:
12g = 1 mol
2.3g = x moles of C
x = 0.192 moles of C
Now we will use Avogadro's constant number, which is 6.02*10^23 particles or atoms, to find how many atoms we have:
6.02*10^23 = 1 mol
x atoms = 0.192 moles
x = 1.15*10^23 atoms of Carbon in 2.3 grams