Context: Hydrogen has three naturally occurring isotopes, denoted 1H, 2H and 3H. Other, highly unstable nuclei (4H to 7H) have been synthesized in the laboratory but not observed in nature.

Question: How many natural isotopes does hydrogen have>
Answer: 3H

Question: What are the names of these isotopes?
Answer: denoted 1H, 2H and 3H

Question: Which isotopes have unstable nuclei?
Answer: 4H to 7H