It means that particular combination of protons and neutrons is not stable.
Your question is meaningless. Radium IS a radioactive element, and its power depends on the context. If you mean "is there an element more radioactive than radium" then yes, there are many, e.g. astatine.
radioactive decay
No, graphite is not radioactive.
No, water is not radioactive.
Yes, it is possible for water to become radioactive if it comes into contact with radioactive materials or is contaminated by radioactive substances.
they are little particle that eat for breakfast
cool
no
I suppose you must mean uranium, it is slightly radioactive.
its nuclei can split apart
Radioactive Iodine
That the substance is dangerous & explosive.
Do you, perhaps, mean "radioactive"? Yes, radioactive materials can be hazardous. If you literally mean "radiant", i.e. glowing, that's not technically in itself a hazard.
It depends what you mean. The chemicals which are radioactive may react with yeast, but no because they are radioactive; merely because they are chemicals. The radiation can kill the yeast, but this is not "reacting".
If an element is radioactive, it refers to the stability of their atomic nucleus. If that atomic nucleus is not stable, it is considered radioactive.
The meaning of radioactive is: an unstable element which emit radiations as alpha, beta, gamma etc.
Radioactive Iodine Uptake