Concept:The low melting and boiling points of covalent molecules depend on the strength of the forces between the molecules, not within them.
Explanation:Covalent molecules are held together by strong intramolecular covalent bonds.
However, the forces between separate molecules are weak intermolecular forces.
These weak forces require only a small amount of heat energy to overcome.
So, covalent molecular substances melt and boil easily at low temperatures.
For example, simple molecular substances like iodine and carbon dioxide have low melting points.
The three-dimensional shape or shared electron pairs do not control melting point.
Melting point depends mainly on the weak forces of attraction between molecules.
Answer:A. They have weak intermolecular forces.