The correct option is B 64 L
For an adiabatic process q=0,
From the First law, ΔU=q+w
For an adiabatic irreversible process, w=−Pext(V2−V1)
w=△U=P2V2−P1V1γ−1
⇒−Pext(V2−V1) = P2V2−P1V1γ−1
For a monoatomic gas, γ=1.67
⇒−1(V2−10) = 1×V2−10×10γ−1
⇒10−V2 = V2−1000.67
⇒(10−V2)×0.67=(V2−100)
⇒V2=63.89 L=64 L