The deviations from ideal gas behaviour `PV =RT` were successfully explained by van der Waals he pointed out that it is not advisable to neglect the volume of molecules and attractions between themselves at all the conditions He proposed volume correction and pressure correction as `(V -b) and ( P+(a)/(V^(2)))` for 1 mole of gas in ideal gas equation .
Compressibility factor for a real gas `Z` at average pressure is .
A. `1+RT`
B. `1+(Pb)/(RT)`
C. `1 -(a)/(RTV)`
D. `1`