मानव शरीर का सबसे कठोर पदार्थ कौन सा है?

उत्तर: (A) दाँत का इनैमल / Tooth enamel — Tooth enamel is the hardest substance (96% calcium phosphate/hydroxyapatite). It is harder than bone. Despite hardness, acids (from bacteria) dissolve enamel causing cavities. Fluoride strengthens ena...