A sample containing \(n\) moles of a monatomic ideal gas is initially at pressure \(P_0\), volume \(V_0\), and absolute temperature \(T_0\). The gas expands isobarically at pressure \(P_0\) to a final volume of \(2V_0\) by absorbing energy from a thermal reservoir maintained at a constant temperature \(T_{\text{res}} = 2T_0\). Which of the following expressions represents the change in entropy of the thermal reservoir, \(\Delta S_{\text{res}}\), during this expansion?