b. the carbon atoms in diamond have a lot of strong covalent bonds with other carbon atoms. which are conjoined in a 3d structure. This means the ‘giant covalent structure’ of diamonds is very difficult to break, making diamonds very hard.
However, the carbon atoms in graphite have less covalent bonds, and graphite is structured in sheets of atoms with weak forces holding them together - this means these sheets can slide off easily and come apart from the structure. Therefore, graphite is very soft.
