He model below shows a calcium atom. An image has a mix of red and blue balls in its center and 4 concentric black rings around the center. The first ring from the center has 2 small green balls on it. The second ring has 8 small green balls on it. The third ring has 8 small green balls on it. The outermost ring has 2 small green balls on it.

How many electrons are in the third energy level?

2
8
18
20