D

Step 1: Understand the property of superconductivity.
Superconductivity refers to a phenomenon where a material exhibits zero electrical resistance and the expulsion of magnetic fields below a certain temperature, known as the critical temperature.
Step 2: Identify the behavior of conductance in superconductors.
In superconductors, the conductance increases dramatically, leading to infinite conductance as temperature approaches absolute zero.
Step 3: Compare with other options.

• Thermal conductivity relates to the flow of heat, not electricity.
• Optical conductivity pertains to a material's response to electromagnetic waves.
• Magnetic conductivity is not a standard term used in physics.

Therefore, the correct answer is D: Superconductivity.