Answer:
B. They have low melting and boiling points.
Covalent compounds typically have low melting and boiling points compared to ionic compounds. This is because covalent compounds are formed by the sharing of electrons between atoms, resulting in the formation of discrete molecules. The intermolecular forces holding these molecules together are generally weaker compared to the strong electrostatic forces between ions in ionic compounds. As a result, less energy is required to break the intermolecular forces and convert a covalent compound from a solid to a liquid or gas, leading to lower melting and boiling points.