This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
In reversible hydrocolloid the property by which the transformation from sol to gel and gel to sol occurs, is a function of the: 
Select and explain. 
A. Concentration of fillers and plasticizer, B. Percentage composition by weight of water, C. Concentration of potassium sulphate, D. Temperature
D: Temperature
Answer: D: Temperature 
Explanation: The physical change of agar from sol to gel is induced by lowering the temperature. The gel liquefies to a sol when it is heated to a temperature known as the liquefaction temperature (70°C to 100°C). When the sol is cooled, it becomes a gel at a point known as the gelation temperature (between 37°C and 50°C). Thus, it is called a reversible hydrocolloid. The gelation temperature is critical for impression making.
Phillips dental materials 12th edition page no 168,170