a balloon is filled with 500 mL of helium at a temperature of 27 degrees celsius and 755 mmHg as the balloon rises in the atmosphere the pressure and temperature drop what volume will it have when it reaches an altitude where the temperature is -33 degrees celcius and the pressure is 0.65 atm

Answer 1

(P1V1/T1) = (P2V2/T2)
Remember T must be in kelvin.
It's difficult to read sentences, especially in technical areas such as chemistry, when one has a problem knowing where sentences begin and where they end.
BTW, note e the correct spelling of celsius.

Answer 2

I got the answer of 465mL...(is this correct)

Answer 3

I don't get that. Did you use kelvin for both T? Did you convert 0.65 atm to mm Hg (or convert 755 mm Hg to atm?)
Post your work and I'll find the error for you.