The hardest substance of human body is _________

Enamel is the hardest substance in the human body. It is the highly mineralized outer layer of the tooth, primarily composed of crystalline calcium phosphate (hydroxyapatite).

Dentin is the layer beneath the enamel, which is less hard.

Cementum is a calcified substance covering the root of a tooth.

Histone is a protein that provides structural support to a chromosome.

Answer: enamel