c
(c) In a cyclic, $\Delta U = 0 $
From FLOT, $\Delta Q = \Delta U + \Delta W = 0 + \Delta W = $ Area of closed curve
==> $\Delta$ Q = $\pi r^2$ = $\pi {\left( {\frac{{20}}{2}} \right)^2}k{P_a} \times litre$ $ = 100\,\pi \times {10^3} \times {10^{ - 3}}J = 100\,\pi J$