For the purpose we will here use the ideal gas law:
p×V=n×R×T
V= 5.0 L
T= 373K
p= 203kPa
R is universal gas constant, and its value is 8.314 J/mol×K
Now when we have all necessary date we can calculate the number of moles:
n=p×V/R×T
n= 203 x 5 / 8.314 x 373 = 0.33 mole