For a spontaneous process, in a reaction

For a spontaneous process, $\Delta S_{\text{total }}>0$. From the second law of thermodynamics, all spontaneous processes are irreversible and are accompanied with an increase in total entropy S. The entropy of an isolated system increases in the course of a spontaneous change.

$\Delta {\mathrm{S}}_{\text{total }}=\left(\Delta {\mathrm{S}}_{\text{system }}+\Delta {\mathrm{S}}_{\text{surroundings }}\right)>0$.

Therefore, option C is correct.