A) When 2.50 g of SO2 is heated with excess oxygen, 2.50 g of SO3 is obtained.
2SO2 + O2 → 2SO3

1. and 2. question: in which equation? or i don't understand you, 3. a), 4. c), 5. c), 6. b), 7. d), 8. d) if small number is underlined(behind symbol) , b) if big number is underlined(in front of symbol)9. what is underlined there? 10. c)

The answer is 323 g.

257 grams h2o i think