Concept:High melting and boiling points signal a giant lattice held by strong electrostatic forces.
Explanation:An electrovalent (ionic) compound forms a giant ionic lattice.
This lattice contains oppositely charged ions attracted by strong electrostatic forces.
A large amount of energy is needed to overcome these forces.
Therefore, electrovalent compounds have high melting and boiling points.
Covalent compounds and dative covalent compounds have weaker intermolecular forces.
Non-metals also generally show low melting and boiling points.
Answer:C. electrovalent compound