A propane stove burned 470 grams propane and produced 625 grams of water (this is the actual yield) C3H8 +5O2=3CO2+4H20. What was the percent yield of water for the stove?

I would really appreciate the help. I don't understand how to begin.

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.

if you mean hydrogen and oxygen then water is the product