Which property is true of covalent molecular substances?

Covalent molecular substances are characterized by their inability to conduct electricity, which is primarily due to the absence of free-moving charged particles, such as ions or delocalized electrons. In these substances, atoms are held together by covalent bonds, forming discrete molecules that do not carry a charge when in solid form. Because they are made of neutral molecules, there are no charged species available to conduct electric current, which is why they do not conduct electricity.

In contrast, other properties associated with covalent molecular substances include lower melting points and relatively weaker intermolecular forces compared to ionic compounds. This distinction is significant because it highlights that while covalent molecular substances may be solid, liquid, or gas at room temperature, their melting points are generally not high, and they do not possess the strong intermolecular forces characteristic of solid ionic compounds. Therefore, the defining characteristic that covalent molecular substances do not conduct electricity due to the lack of charged particles is a key aspect of their behavior and properties.