c
(C)
$n =\frac{ w _{\text {net }}}{ Q _{\text {sup plied }}}$
$w _{\text {net }}=\frac{\pi}{4} \times \frac{ V _0}{2} \times \frac{ P _0}{2}=\frac{\pi P _0 V _0}{16}$
Heat is supplied to the gas only during process $CA$.
$\text { so } Q _{ CA }= w _{ CA }+\Delta U _{ CA }$
$Q _{ CA }=\left(\frac{\pi P _0 V _0}{16}+\frac{ P _0 V _0}{2}\right)+\frac{3}{2} \times P _0 V _0$
$Q _{\text {supplied }}=\frac{\pi P _0 V _0}{16}+2 P _0 V _0$
$n =\frac{\frac{\pi P _0 V _0}{16}}{\frac{\pi P _0 V _0}{16}+2 P _0 V _0}=\frac{\pi}{\pi+32}$
