Radioactive decay question 6 options: is a spontaneous process. occurs when an unstable nucleus loses energy. does not require any input of energy. all of the above

The correct answer is all of the above.  

Nuclear or radioactive radiation or radioactive decay refers to the procedure by which an unstable atomic nucleus loses energy in the form of mass in its rest frame by discharging radiation like a beta particle, alpha particle, or a gamma ray. A substance comprising such unstable nuclei is regarded as radioactive. The process does not need any input of energy.  

that's what i got you can count the number of atoms