What characteristic is crucial for materials used in electronics?

High conductivity is a crucial characteristic for materials used in electronics because it directly influences how well electrical signals can be transmitted through the material. In electronic components, such as semiconductors, conductors, and interconnects, the ability to allow electricity to flow with minimal resistance is essential for efficient operation and performance. Materials with high conductivity, like metals and certain doped semiconductors, ensure that devices operate effectively, perform at high speeds, and consume less energy. This characteristic allows for the rapid movement of electrons, which is necessary for the functioning of everything from microprocessors to circuit boards.

In contrast, the other characteristics listed would not support the necessary performance in electronic applications. Brittleness, for example, would likely lead to material failure under mechanical stress, making it unsuitable for dynamic environments found in electronics. Low density might be advantageous in some contexts, but it does not directly impact electrical performance or conductivity. High opacity is not a beneficial property for electronic materials, as it does not relate to their electrical characteristics and could interfere with optical applications when transparency is desired. Thus, high conductivity stands out as an essential trait for effective electronic materials.