Answer:
C. A gas forms when two liquids are mixed.
Step-by-step explanation:
In a physical change, no change in the composition of the material occurs. There might be change in the state of the matter. Examples of physical changes: Melting, cutting, freezing. option A, B and D are all physical changes.
In a chemical change, the composition of the matter changes. In option C, when two liquids mix, a gas forms which has different composition than the individual liquids.