Answer the following question given this paragraph: We have talked about the activity and decay of individual isotopes. In the real world, there is a decay chain that takes place until a stable end-product is produced. For U-238, the chain is a long one, with a mix of isotopes having very different half-lives. The end of the chain resides in lead, a stable element that does not decay further. Q: What is required for a decay chain to end? Choices: - stable half-life - unstable end-product - radioactive cascade - stable end-product A:
Answer:
stable end-product