GENERAL KNOWLEDGE

Detailed explanation-1: -The structure extends in space and produces a rigid 3-D network of carbon atoms with directional covalent bonds throughout the lattice. It is very difficult to break extended covalent bonding which makes diamond the hardest substance on the earth.

Detailed explanation-2: -The hardest substance is diamond because in diamond each carbon is sp3 hybridized state and is linked to another carbon atoms held at corners of a regular tetrahedron by covalent bonds to form three-dimensional cage-like structure. Due to its strong covalent molecular structure, it is hard.

Detailed explanation-3: -Each carbon atom in a diamond contains four electrons in its outer shell, which are shared by covalent connections with four other carbon atoms. This arrangement aids in the formation of a tetrahedral crystal that is rigid. Diamond is one of the hardest things on the planet because of its densely linked structure.