Which substance can conduct electricity under certain conditions?

The correct answer is a substance classified as a semiconductor. Semiconductors have unique properties that allow them to conduct electricity under specific conditions. This is typically due to the presence of impurities or temperature changes, which can create free charges within the material. Unlike conductors that always allow electricity to flow freely, semiconductors can be modified to increase their conductivity.

For example, silicon is a common semiconductor used in electronics, and when doped with certain materials, it can switch from an insulating state to conducting electricity. This ability to control electrical conductivity makes semiconductors essential in modern technology, including in the manufacturing of transistors, diodes, and solar cells.

In contrast, insulators resist electrical flow, conductors allow electricity to pass without restrictions, and resistors are designed to resist the flow of electricity and limit current in a circuit. Each of these substances has distinct roles and characteristics in electrical applications, with semiconductors providing a critical middle ground between insulating and conducting materials.