Charles law states that for a fixed mass of gas at constant pressure the volume of the gas is directly proportional to the temperature in Kelvin scale
v1/T1 = v2/T2
Where v1 is volume and T1 is temperature at the first instance
v2 is volume and T2 is temperature at the second instance
Substituting the values in the equation
0.5 L / 203 K = v2 / 273 K
v2 = 0.672 L
The volume of Air after heating is 0.672 L