Which of the following is NOT a conductor?

Hard rubber

The correct answer is option 1. Hard rubber.

The material among the options provided that is NOT a conductor is Hard rubber.

Hard rubber is an insulator or non-conductor of electricity. It does not allow electric current to flow through it easily. In contrast, copper, silver, and nickel are all metals known for their high electrical conductivity. They allow electric current to flow through them with minimal resistance.