Which material has the lowest thermal conductivity?

Thermal conductivity refers to a material's ability to conduct heat. Air, being a gas and having a low density, has the lowest thermal conductivity among the listed materials. It is a poor conductor of heat due to the large spaces between air molecules, which diminishes the transfer of thermal energy.

In contrast, aluminum, brass, and copper are all metals, characterized by their tightly packed atomic structure, which allows for efficient conduction of heat. Metals generally have high thermal conductivity because they contain free electrons that can transfer energy rapidly between atoms. Therefore, when comparing air to metals like aluminum, brass, and copper, air is significantly less effective at conducting heat, making it the correct choice for having the lowest thermal conductivity.

Understanding thermal conductivity is essential in various applications, including insulation materials, where low thermal conductivity is desired to prevent heat transfer.