The process by which a liquid is separated and changed into a soft, semi-solid substance is called:
curdling
The explanation for the correct option:
Option C: Curdling is a process in which a liquid is separated and changed into a soft, semi-solid substance.
The explanation for the incorrect option:
Option A: Sublimation is a process in which a solid substance is directly changed into a gaseous state.
Option C: Evaporation is a process in which a liquid is changed into a gaseous state.
Option D: Freezing is a process in which liquid is changed into solid-state.
Therefore, Option C is correct, i.e. Curdling.