Its nucleus is unstable.
Yes. A radioactive atom is a radioactive atom. If that atom exists as a single atom and is uncombined and it is radioactive, it's radioactive. If that same atom is chemically combined with another or other atoms, it's still radioactive. It's just that simple.
No, it's called "radioactive." "Retroactive" is something that's active in regards to the past.
A radioactive atom is an atom of an element with an unstable nucleus.
They originate in the nucleus of the atom.
The initial atom is transformed in another atom.
No, not always.
unstable, radioactive
An atom whose nucleus decays over time is called radioactive. Some examples of radioactive substances are uranium, plutonium, and einsteinium.
smaller than the original atom and possibly radioactive
It is a radioactive element.
radioactive decay
Radioactive atoms are atoms that have unstable nuclei, which can undergo radioactive decay to become more stable. During this process, they emit radiation in the form of alpha particles, beta particles, or gamma rays. This emission of radiation can cause a change in the atom's composition or energy level.