Answer: 278grams, assuming N,O is actually N2O.
Explanation: Is "N,O" really supposed to read NO or N2O? This assumes N2O, laughing gas. I see another post used NO, so the problem is covered either way.
The molar mass of N2O is 44 g/mole. 765g would be 17.38 moles of N2O. That means we also have 17.38 moles of O. The molar mass of O (not O2) is 16 g.mole.
(17.38 moles(*(16 g/mole) = 278 grams of O
Another approach is to calculate the percentage of O in N2O:
N: 2*14 = 28
O: 1*16 = 16
N2O: = 44
% O is 16/44 = 36.3%
0.363*765 = 278 grams (same answer)
