Why is it impossible to predict when an individual unstable nucleus will decay?

The correct answer is A: Because decay is a random process.

The correct answer is A: Because decay is a random process. This supports the learning objective "Determine half-life from a decay graph." in Half-lives and the random nature of radioactive decay because it uses the correct atomic and nuclear radiation relationship for Atoms and nuclear radiation. The other options are less suitable because they do not match the required Half-lives and the random nature of radioactive decay idea: Because all nuclei decay at the same time; Because it depends on external factors; Because decay rates are constant.