Chemistry is not a strong point for me, but here's my take on this rather cryptic question.
3.01E23 is half a mole worth of atoms. If you go to the periodic table and select an element, say magnesium, you will find its atomic mass as 24.31. That means that one mole of magnesium atoms weighs 24.31 grams. So half a mole would weigh half that, like 12.155 grams.
Need that atomic mass to make the question work, me thinks Miaaaa
Cheers
+118654 
