$0.2$ moles of an ideal gas, is taken rouna the cvcle $a b c$ as shown in the figure. The path $b-c$ is adiabaric , ness, $a-b$ is isovolumic process and $c-a$ is isobaric process. The temperature at ' $a$ ' and ' $b$ ' are $T_{a}=300 \mathrm{~K}$ and $\quad T_{b}=500 \mathrm{~K}$
and pressure at ' $a^{\prime}$ is 1 atmosphere. The volume at $' c^{\prime}$ is :
(Given: $\gamma=\frac{C_{P}}{C_{V}}=\frac{5}{3}$, $R=8.205 \times 10^{-2}$ litre/atm/mol-K)
(a) $6.9 \mathrm{~L}$
(b) $6.68 \mathrm{~L}$
(c) $5.52 \mathrm{~L}$
(d) $5.82 \mathrm{~L}$