What alternates in alternating current

Alternating current, is an electric current which periodically reverses direction, whereas direct current flows only in one direction. AC is the form in which electric power is delivered to businesses and residences, and it is the form of electric energy that consumers typically use when they plug kitchen appliances, televisions and electric lamps into a wall socket. A common source of DC power is a battery cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.

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Your answer is c. explanation: plasma  is the fourth state of matter, derived from the gaseous state of matter.  plasma  can contain free  electrons  and/or  ions. while  plasma is never neutral, it can either be positively or negatively charged.  gases, however, are electrically neutral.