The best definition of superconductor is:*1 pointIt is a materials showing perfect conductivity and Meissner’s effect below a critical temperatureIt is conductor having zero resistanceIt is a perfect conductor with highest diamagnetic susceptibilityIt is a perfect conductor but becomes resistive when a current density through it exceeds a critical value

The best definition of a superconductor is: It is a material showing perfect conductivity and Meissner’s effect below a critical temperature.

Here's why:

1. Superconductors are materials that can conduct electricity with no resistance. This is known as perfect conductivity.

2. The Meissner effect is a phenomenon where a superconductor will expel a magnetic field from its interior when it is cooled below its critical temperature. This is a unique property of superconductors.

3. The critical temperature is the temperature below which a material must be cooled to exhibit superconductivity.

4. While it's true that superconductors have zero resistance and high diamagnetic susceptibility, these are properties of superconductors, not the definition.

5. The statement "It is a perfect conductor but becomes resistive when a current density through it exceeds a critical value" is not entirely correct. Superconductors can carry large amounts of current without becoming resistive, as long as they are below their critical temperature.