If a balloon is filled with 20 cc of air at 25 celsius what will its volume be at 0 celsius?

Using the ideal gas law: PV = nRT; and given the initial conditions:

V1 = 20 cc

T1 = 25 C or 298 K

We are asked to determine the volume at 0 C or 273 K. Assume that the pressure and number of moles are constant. Thus,

V/T = constant, then

V1/T1 = V2/T2

Solve for V2:

20 cc / 298 K = V2 / 273 K

V2 = 18.32 cc