The significance of the half-life of a radioisotope tells what fraction of a radioactive sample remains after a certain length of time (option D)
How to determine the significance of the half-life of a material?
The half-life a radioactive substance is the time taken for half the radioactive substance to decay.
This implies that the half-life will tell how much of the radioactive substance will remain over a given time frame
Now lets take a look at the options given from the question. These are highlighted below:
A. It tells how long a radioisotope sample is considered dangerous.
B. It tells what kind of radioactivity is released through radioactive
decay.
C. It tells how much energy is released over the lifetime of a
radioactive sample.
D. It tells what fraction of a radioactive sample remains after a
certain length of time.
We can see that only option D correspond to the definition of half-life
Thus, we can conclude that the correct answer is option D