Multiple choice general knowledge science & technology What is the hardest substance in the human body Tooth Enamel Bones Bone Marrow Toe Nails Reveal answer Fill a bubble to check yourself A Correct answer Explanation Tooth enamel is the hardest substance in the human body, rating 5 on the Mohs scale. It is primarily composed of hydroxyapatite minerals, making it harder than bones, bone marrow, or nails.