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
Hardening solution for agar: 
Select and explain. 
A. Titanium flouride., B. Sodium flouride., C. 2% potassium sulphate., D. All of the above.
C: 2% potassium sulphate.
Answer: C: 2% potassium sulphate. 
Explanation: Gypsum products are not compatible with the hydrocolloid impression materials. The casts will become soft. This can be prevented by incorporating hardening solutions in the impression material during manufacturing or by immersing the impression in an accelerator solution for the setting of gypsum.
The hardening solutions are 2% potassium sulphate for agar and titanium fluoride for alginate materials.