Which explanation best describes the behavior of compounds with simple molecular structures when heat is applied?

Compounds with simple molecular structures typically consist of molecules held together by relatively weak intermolecular forces such as van der Waals forces. When heat is applied to these compounds, the energy provided facilitates a phase change, such as melting or boiling, without significantly breaking the covalent bonds that hold the atoms within the molecules together. This phase change occurs with relatively low energy input compared to ionic or covalent compounds that have stronger bonding forces.

For example, when heating a simple molecular solid like ice (solid water), it transitions to liquid water at 0°C with minimal energy requirement compared to breaking down the water molecules themselves. This characteristic behavior makes these substances distinct in their response to heat, allowing them to change from solid to liquid or liquid to gas with lower energy compared to other types of compounds that have stronger bonding networks.

The other options do not accurately characterize the behavior of simple molecular compounds under heat. The dissolution in water is related to solubility rather than thermal behavior, breaking down into smaller molecules typically requires more energy and is not characteristic of compounds like water or simple covalent substances, and vigorous reactions with air are not a hallmark of simple molecular structures, as they often do not react this way at all.