Which of the following materials is a poor conductor of heat?

Glass is considered a poor conductor of heat primarily due to its molecular structure, which does not allow for the efficient transfer of thermal energy. Unlike metals such as copper and aluminum, which have free electrons that can move easily and transfer heat quickly, glass has a more rigid structure that restricts the movement of its molecules. This makes it act as an insulator rather than a conductor.

In applications where heat conduction is required, materials that facilitate the rapid transfer of heat, such as metals, are preferred. Copper and aluminum are excellent conductors because their atomic structure allows electrons to move freely, enabling quick heat transfer. Cast iron, while not as efficient as copper or aluminum, still conducts heat better than glass due to its metallic nature and the presence of iron atoms, which have some level of electron mobility.

Therefore, glass stands out as a poor conductor of heat in comparison to the other options listed.