Multiple choice general knowledge science & technology Among the various allotropes of carbon, coke is the hardest, graphite is the softest diamond is the hardest, coke is the softest diamond is the hardest, graphite is the softest diamond is the hardest, lamp black is the softest Reveal answer Fill a bubble to check yourself C Correct answer Explanation Diamond is the hardest known natural material due to its strong covalent bonds in a 3D tetrahedral structure. Graphite is extremely soft because its layers are held by weak van der Waals forces, allowing them to slide easily.