The Half-Life of a Radioactive Nuclide Is

The half-life of a radioactive nuclide is

A) that period of time in which 25% of the original number of atoms undergoes radioactive decay.
B) the time at which the isotope becomes nonradioactive.
C) that period of time in which 50% of the original number of atoms undergoes radioactive decay.
D) the period of time it takes to reduce the radioactivity by 100%.
E) none of the above