Many stereo speaker cables are made of copper wire surrounded by rubber. The electricity travels down the copper portion of the cable while the rubber protects you from being "zapped" by the electricity. Which physical property explains the difference in ability of copper and rubber to transmit electricity?

Conductivity.

Explanation:

Conductivity is the physical property that explains the difference in ability of copper and rubber to transmit electricity. Basically transmission of electricity or electric current is possible due to the movement of electrons. There are free electrons in the copper while in rubber there are no free electrons. When electrons move in the direction, an electric current flows in the opposite direction. This phenomenon is also known as conductivity i. e. ability to conduct current.