In the diagram bellow, an ideal pendulum released from position a swings freely to position b. as the pendulum swings from a to b, it's mechanical energy (1) decreases, then increases (2) increases, only (3) increases, then decreases (4) remains the same

Well you have not attached the diagram so I'm going to have to make a few wild guesses here. If all you had to do was release it from A and it headed for B on its own then it must have had some potential energy at A ... otherwise it would have just stayed there when it was released. So it's beginning to look like A is off to the side and B is the center of the swing. After the pendulum is released its total mechanical energy doesn't change. It just transforms back and forth from potential energy to kinetic energy and back again to potential energy. But the total is constant.

Alkaline earth metals are found in group 2 of the periodic table.