<prompt> The recommended concentration of acidulated phosphate APF fluoride gel is:281.2310  <response>: 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 Brudevolds solution.Essentials of preventive and community dentistrySoben Peter5th editionpage no. 258 