Nitroglycerin (C3H5N3O9) is a powerful explosive. Its decomposition is C3H5N3O9=6N2+12CO2+10H2O+O2. What is the number of O2 molecules from 2 x 10^2 grams of nitroglycerin? What is the % yield if 6.55 grams of O2 were collected?

4C3H5N3O9 -> 6N2 + 12CO2 + 10H2O + O2

This is not balanced! Now it is! Don't forget all coefficients again!

2 X 10^2 grams Nitro (1 mole Nitro/227.1 grams)(1 mole O2/4 mole Nitro)(6.022 X 10^23/1 mole O2)

= 1.33 X 10^23 molecules O2
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1.33 X 10^23 molecules O2 (1 mole O2/6.022 X 10^23)(32.0 grams/1 mole O2)

= 7.05 gram
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6,55 grams/7.05 grams

92.9% is the yield
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I see you have a lot of problems. If you do not try to work some yourself you will fail chemistry. Chemistry is in the doing.