Coal=fire and in the artic its hard to build a fire
Voltage is known to be used as a requirement for stimulating an axon. The axon conducts electrical signals away from the nerve cell. The main function of the axons is that it is specifically used to transmit information, in a form of electrical impulse, to the other parts of the body.
D. Volcanoes formed most of them through eruption.
I believe it is Sodium. I could be wrong though.