How Is the Half-Life of a Radioactive Parent Isotope Defined

Multiple Choice

How is the half-life of a radioactive parent isotope defined?

A) the time it takes for half of the parent isotope to decay
B) half the time it takes for the amount of parent isotope to reach zero
C) the time it takes the parent isotope to go through half the decay steps necessary to produce a stable daughter isotope
D) half of the average rate of decay of the parent isotope