
Work done in complete cycle,
$W=W_{12}+W_{23}+W_{31}$
Given $W=10 \,J , W_{23}=0$ and $W_{31}=-20 \,J$
So, from Eq. $(i)$, we have $W_{12}=30 \,J$
As in isothermal process,
Heat absorbed $=$ Work done
$\therefore$ Heat absorbed in process $1 \rightarrow 2=30 \,J$


$1.$ efficiency more than $27 \%$
$2.$ efficiency less than the efficiency a Carnot engine operating between the same two temperatures.
$3.$ efficiency equal to $27 \%$
$4.$ efficiency less than $27 \%$