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Ductility is the ability of a material to deform or stretch under tensile stress without breaking. Since metallic solids have delocalized electrons, they can easily slide past each other without breaking the bonds. Therefore, ductility is a characteristic of a metallic solid. Covalent-network solids are generally brittle due to their strong, directional covalent bonds; hence, they are not ductile.

Hardness refers to the resistance of a material to localized deformation, such as indentation or scratching. Due to the strong covalent bonds present in covalent-network solids, they exhibit high hardness. In general, metallic solids are softer than covalent-network solids, but some metallic solids exhibit hardness as well, such as tungsten and steel. So, hardness can be a characteristic of both covalent-network solids and some metallic solids.

The melting point refers to the temperature at which a substance changes from a solid to a liquid. A high melting point indicates strong bonds between the atoms or ions. Covalent-network solids have strong directional covalent bonds, which results in high melting points. Metallic solids have metallic bonds involving the delocalization of electrons and also exhibit high melting points. Therefore, a high melting point is a characteristic of both covalent-network solids and metallic solids. In summary: - Ductility: typical characteristic of a metallic solid. - Hardness: typical characteristic of both a covalent-network solid and some metallic solids. - High melting point: typical characteristic of both covalent-network solids and metallic solids.