As an electron gains energy, it becomes excited and jumps to a lower energy level?

Yes if you add an energy to an electron the electron will become excited, and it will jump to its highest level then go back down releasing  energy

This is inccorect. When an electron gains energy and becomes excited it jumps to a higher energy level. When an electron jumps to a lower energy level it de-excites.

14 days is the half-life of phosphorus-32

answer: they produce more slow than unicellular organisms.