The covalent crystals _ have giant molecules that are insoluble in all the solvents.

Explanation

a) Silicon Carbide (SiC): Silicon carbide is a covalent crystal with a giant molecular structure. It consists of a three-dimensional network of covalently bonded atoms. Due to its strong covalent bonds, silicon carbide is insoluble in all solvents. b) Diamond: A diamond is also a covalent crystal with a giant molecular structure. It is composed of carbon atoms arranged in a tetrahedral lattice through strong covalent bonds. Like silicon carbide, diamond is insoluble in all solvents due to its robust covalent bonding. Therefore, both silicon carbide and diamond, being covalent crystals with giant molecular structures, are insoluble in all solvents, making option c) the correct answer.