Answer
$\Delta S=6.34\frac{J}{K}$
Work Step by Step
For isothermal process:
$Q=W=nRT\ln(\frac{V_f}{V_i})$
$\implies \Delta S=\frac{Q}{T}=\frac{W}{T}=nR\ln(\frac{V_f}{Vi})$
Therefore;
$\Delta S=nR\ln(\frac{V_f}{Vi})$
We plug in the known values to obtain:
$\Delta S=0.55(8.31)\ln(\frac{0.800}{0.200})=6.34\frac{J}{K}$
