Question

# Diamond is a A.solid containing hydrogen bonds B.ionic solidC.covalent solidD.metallic solid

Hint: We must know that diamond and graphite both are the allotropes of carbon and so they have identical chemical properties. In diamond, each atom here shares the electrons with 4 other carbon atoms. Diamond is very strong in comparison to graphite as graphite exhibits a brittle and soft state. The sheets of carbon become bonded with weak covalent bonds during a tetrahedral structure. The other sheets of carbon become bonded by weak intermolecular forces. Due to the weak intermolecular forces, the layers of graphite can slide upon each other and make the substance very weak in comparison with diamonds. Also, diamond is difficult to break due to its giant covalent lattice and its many strong covalent bonds.

Diamond is a network covalent solid with no molecular boundaries.
Explanation:
Diamond is a naturally occurring mineral that is completely composed of only carbon atoms. Each carbon atom in a diamond is surrounded by four other carbon atoms and connected to one another by strong covalent bonds. Such an arrangement of covalently bound carbon atoms in the tetrahedral array makes the diamond structure the toughest substance.
Covalent bonds are the strongest type of chemical bond.
To break up the solid structure of a diamond, a lot of energy has to be forced to break the covalently bound strong $C - C$ bonds. Diamond is a network solid and is a never-ending repetition of carbon atoms bonded to each other by covalent bonds.

As we can see in this above diagram, a perfect single crystal of a covalent solid of diamond thus makes a single giant molecule and it is a network covalent solid with no molecular boundaries.
Thus, Diamond is a covalent solid.
Hence, option C is the correct option.