Final answer:
Compound A is a covalent compound, Compound B is a metallic compound, and Compound C is a molecular compound.
Step-by-step explanation:
Compound A, which is crystalline, has a high melting point and becomes more conductive when dissolved, is likely a covalent compound. Covalent compounds are characterized by their strong bonds between nonmetal atoms. They have high melting points due to the strength of these bonds and are usually insoluble in water. They also do not conduct electricity well, both as solids and in solution.
Compound B, which is highly conductive and malleable, is likely a metallic compound. Metallic compounds have delocalized electrons that can move freely throughout the structure, allowing for high electrical conductivity. They are also malleable, meaning they can be easily shaped or deformed.
Compound C, which is not highly conductive and is gaseous, is likely a molecular compound. Molecular compounds are composed of individual molecules held together by covalent bonds. They have low electrical conductivity and can exist as gases at room temperature.