Which characteristic is essential for an electrical box installed in a fire-resistive assembly?

The correct answer is that the electrical box must be listed for fire-resistive use. This requirement is critical because fire-resistive assemblies are designed to contain and delay the spread of fire, ensuring safety and compliance with building codes. An electrical box that is specifically listed for this purpose has been tested and certified to meet certain fire resistance standards, which helps maintain the integrity of the fire-resistive assembly. This contributes to the overall safety of the structure by preventing potential fire hazards associated with electrical installations.

The other options do not directly address the necessary characteristics for maintaining fire-resistive qualities. While using plastic might be acceptable in some contexts, it does not inherently ensure fire resistance. Surface mounting is not a requirement for fire-resistive assemblies, and while grounding is crucial for electrical safety, it does not relate to the fire-resistive characteristics of the box itself. Thus, ensuring that the box is listed for fire-resistive use is paramount for maintaining the safety and compliance of the installation in fire-resistive assemblies.