The correct option is D R
We know that, for polytropic process of index x,
PVx=constant
Molar heat capacity is given as,
C=CV+R1−x
⇒C=fR2+R1−x ...(1)
f=3 [monoatomic gas]
x=3 [PV3=constant,x=3]
On putting these values in Eq.(1)
⇒C=3×R2+R1−3
⇒C=3R2−R2
⇒C=R
The molar heat capacity of the gas during the given process is R