d
The work done in expansion of gas
$\mathrm{W}=\mathrm{nRT}\, \ell n \frac{\mathrm{V}_{\mathrm{f}}}{\mathrm{V}_{\mathrm{i}}}=\mathrm{nRT}\, \ell n \frac{\mathrm{P}_{1}}{\mathrm{P}_{\mathrm{f}}}$
The work done on the gas
$=-n R T \ell n\left(\frac{P_{f}}{P_{1}}\right)$