Which of the following is a characteristic of electrically conductive materials?

Electrically conductive materials are characterized by their ability to allow the flow of electrical charge, which is generally due to the presence of free electrons or ions within their structure. This property is fundamental to materials like metals, which have a lattice structure that permits the movement of electrons when an electric field is applied.

In addition to electrical conductivity, these materials also typically permit thermal conductivity, allowing heat to pass through them effectively. For instance, metals such as copper and aluminum are known for both their electrical and thermal conductive properties. The ability to conduct electricity is often linked to the mobility of charge carriers, making option C the defining characteristic of these materials.

The other options, while they may describe certain conductive materials, are not universal characteristics. For example, while many conductive materials are solid at room temperature, there are exceptions such as mercury, which is a liquid. Similarly, although some conductive materials may have high melting points, others like indium do not. Lastly, the resilience of a material under stress does not directly relate to its electrical conductivity; some conductive materials may indeed alter their properties under stress. Hence, the defining characteristic is best captured by the ability to allow the flow of heat and electricity.