why are inner transition metals radioactive?

Question

also hwy are noble gases not radioactive?

Answer 1

I don't know what you mean by the "inner transition metals." In general, nuclear stability decreases with increasing atomic weight, which is why the actinidies in particular are highly radioactive, and also the reason why the man-made "trans-uranic elements" are so unstable so as to generally decompose in milliseconds or less.

Many elements also have radioactive isotopes, but this has nothing to do with "inner transition metals." Hydrogen, carbon, nitrogen, and oxygen, for example, all have naturally occuring radioactive isotopes. More radioactive isotopes tend to exist for elements with higher atomic weights, but again, no particular correlation to being a metal or not. One of the ones which is a big worry for many people is radon, which is a noble gas.