Which best describes the materials that make up an electrical cord?
a metallic conductor lacking free electrons surrounded by a rubber insulator with free electrons
a metallic conductor with free electrons surrounded by a rubber insulator lacking free electrons
a metallic insulator with free electrons surrounded by a rubber conductor lacking free electrons
a metallic insulator lacking free electrons surrounded by a rubber conductor with free electrons

a metallic conductor with free electrons surrounded by a rubber insulator lacking free electrons

Explanation: An electrical cord is supposed to transfer electrical charge from a power source to an electrical device. Thus, so as to transfer the charge, we need to have a conductor with free electrons.

However, so as to avoid loss while transmission as well to prevent electrical shocks, it needs to be wrapped by an insulating material. The insulating material should not be a conductor of electricity and thus it should not have any free electrons to avoid transmission of electrical charge.

if you already have the answer to (a), then just work out how many periods there are in 1 minute, and that's the answer to (c).