How many electrons does the 2nd main energy level hold when it is full?

8 electrons

Each principal energy level can contain up to 2n2 electrons, where n is the number of the level. Thus, the first level can contain up to 2 electrons, 2(12) = 2; the second up to 8 electrons, 2(22) = 8; the third up to 18, 2(32) = 18; and so on.

Explanation:

a plasma is a warm ionized gasoline consisting of approximately equal numbers of definitely charged ions and negatively charged electrons. the characteristics of plasmas are notably unique from the ones of ordinary neutral gases in order that plasmas are considered a awesome "fourth kingdom of remember."