+53 My apologies, this is if you were counting the total atoms, not molecules. I found this to be really complex and I'm not even completely sure how to do it. However, my info is from this site and I will attempt to answer this question. https://www.chem.wisc.edu/deptfiles/genchem/sstutorial/Text4/Tx44/tx44.html
One mole of oxygen is 16 grams, so here's a formula to possible solve it.
$${\frac{{\mathtt{6.02}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{{\mathtt{23}}}}{{\mathtt{16}}}} = {\frac{{\mathtt{n}}}{{\mathtt{8.5}}{grams}}}$$
So I'm thinking it's: $${\frac{{\mathtt{51.17}}{\mathtt{\,\times\,}}{{\mathtt{85}}}^{{\mathtt{23}}}}{{\mathtt{16}}}}$$
This is the total atoms you should get, if the formula is correct. If you want molecules, just divide the whole thing by 2 because there are 2 oxygen atoms in one molecule of oxygen gas.
I'm not sure. This is probably wrong, but I hope this helps or at least gives you an idea on how to do it. Good Luck!