Conversation so far:
what is the mass of 2 molecules of nitrogen dioxide?
(2molecules of NO2/1)(46.005gNO2/6.022*10^23 molecules of NO2)=1.5335*10^-22 g of NO2
what is the pass percent of nitrogen in nitrogen dioxide?
30.45%

Question: what is the mass percent of oxygen?
Self-contained rewrite: what is the mass percent of oxygen in nitrogen dioxide?