correct answer is Lightning because it is the naturally occurring electrostatic discharge, during 2 electrically charge field in atmosphere and on the ground temporarily equalize themselves and they instantly release energy.
As it is released cloud so we called it lightning but a spark is generated when the electric field strength is sufficient to ionize the molecules of air, creating a small conduction path through the air.
This is usually a cascade process, because free electrons accelerate in the electric field and ionize more molecules by colliding.
