You will be given a definition of a task first, then some input of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: Radioactive decay is the process in which unstable nuclei become stable by emitting particles and energy and changing to different elements. There are three types of radioactive decay: alpha, beta, and gamma decay. Each differs in what is emitted, how far it can travel, and what it can penetrate. Answer: radioactive decay
Output:
What is the process in which unstable nuclei become stable by emitting particles and energy and changing to different elements called?