One mole of an ideal diatomic gas undergoes a transition from A to B along a path AB as shown in the figure. The change in internal energy of the gas during the transition is:

ΔU=nCvΔT
where n is no. of moles, Cv is heat capacity at constant volume and ΔT is temperature change
for diatomic gas Cv=3/2R
from ideal gas equation T1=P1V1/R and T2=P2V2/R
ΔU=Cv(T2−T1)
ΔU=3/2R(P2V2/R−P1V1/R)
ΔU=3/2(P2V2−P1V1)=−14 kJ
hence correct answer is option C