B

Dental enamel is ~96 wt % mineral, almost entirely hydroxyapatite (calcium-phosphate), whereas dentine (~70 %), bone (~60 %) and gingiva are far less mineralized. Therefore, enamel contains the highest concentration of phosphate among the listed tissues [Bonar 1991, PMID 1666806; Baldassarri 2008, PMID 18573984].