If 16.5 g of oxygen gas is required to inflate a balloon to a certain Volume at 26.5 degrees Celcius, what mass of oxygen gas is required to inflate the same balloon to the same volume and pressure at 10.0 degrees Celcius?

Answer 1

Note the correct spelling of celsius.
I would do the following although it may be the long way around.
Use PV = nRT. Make up a number for V(say an easy number like 1 L) and solve for P. Then substitute that P and the new T and solve for n = number of moles for the new filling. Then n = grams/molar mass and solve for grams. I think the answer is close to 17 grams but that is approximate.