A reactor produces a certain unstable nuclide in a spent fuel rod which is removed from the reactor. Suppose the half-life of this nuclide is 2.5 years. After 20 years what fraction of the original nuclide still remains?

Iknow the first part it is the average star i am not 100% sure

stands for electromotive force and it is measured in volts. despite its name, it is not actually the force in the sense of being a "pushing" or "pulling" (not measured in newtons).an equation that relates emf,  ℰ,  to a battery's terminal voltage, v, current, i, and internal resistance, r, is    ℰ = v + irin this case, the emf can be interpreted as a voltage—a difference in electric potential.i would not say that it would be considered an energy. if emf can be defined as the energy/work per a unit charge from a battery or other electric source, then it is not strictly energy.