Correct Answer - B
As p- V diagram is a straight line passing through origin , therfore, `ppropV" or "pV^(_1)` = constant .
In the process , `pV^(x)` = constant, molar heat capacity is
given by , `C=(R)/(gamma-1)+(R)/(1-x)`
Where , `x=-1` here and `gamma=1.4` for diatomic gas
`C=(R)/(1.4-1)+(R)/(1-(-1))`
`=(5)/(2)R+(R)/(2)=3R`