The correct option is B 0.032
Given : Volume, V = 821 mL = 0.821 L
Temperature, T = 300 K
Total pressure, Ptotal=1 atm=760 torr
Vapour pressure of H2O, PH2O=30 torr
Ptotal=PN2+PH2O
760 torr=PN2+30 torr
PN2=730 torr=730760 atm
Using the ideal gas equation, moles of N2(g) in moist gas mixture is:
nN2=PN2VRT
nN2=(730760)×0.8210.0821×300=0.032
Hence, the correct answer is option (b).