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
The recommended concentration of acidulated phosphate (APF) ﬂuoride gel is: 
Select and explain. 
A. 2%, B. 8%, C. 1.23%, D. 10%
C: 1.23%
Answer: C: 1.23% 
Explanation: An aqueous solution of acidulated phosphate fluoride is prepared by dissolving 20 grams of sodium fluoride in 1 liter of 0.1 M phosphoric acid and to this is added 50% hydrofluoric acid to adjust the pH at 3.0 and fluoride ion concentration at 1.23%.
It is also called as Brudevold's solution.

Essentials of preventive and community dentistry
Soben Peter
5th edition
page no. 258