Describe a process in which energy changes form at least two times explain how the law of conservation of energy applies to the process you describe

A pendulum.  Hold it high and it has potential energy but no kinetic energy because it is still.  As it moves down when you drop it, it changes to kinetic energy and moves faster and faster until it's at the bottom where it has no potential energy.  However, it still has momentum, so now it is changed to potential energy as it moves up the other side

Cations are positively charged ions.  Some biological important Cations are Na+1, Zn 2+, Ca 2+.