$M \mathrm{~kg}$ of a liquid at a temperature $T_{1}$ is mixed with $M \mathrm{~kg}$ of the same liquid at another temperature $T_{2}$ in an isolated tank at constant pressure. The mass specific heat capacity at constant pressure of the liquid is $c_{P}$, which is a constant. The total entropy change in the process is
- $M c_{P} \ln \left(\dfrac{T_{1}+T_{2}}{2\sqrt{T_{1} T_{2}}}\right)$
- $2 M c_{P} \ln \left(\dfrac{T_{1}+T_{2}}{\sqrt{T_{1} T_{2}}}\right)$
- $M c_{P} \ln \left(\dfrac{T_{1}+T_{2}}{\sqrt{T_{1} T_{2}}}\right)$
- $2 M c_{P} \ln \left(\dfrac{T_{1}+T_{2}}{2 \sqrt{T_{1} T_{2}}}\right)$
