An isotope whose nucleus decays spontaneously and gives off particles and energy is: a radioactive isotope
The isotope of the atom of a chemical element is an atom of the same element with the same number of protons but with a different number of neutrons, therefore the atomic mass of an element varies according to its isotope
What is an atom?
The atom is the smallest part of the composition of matter, it is indivisible and is composed of a nucleus that has protons and neutrons, and around the nucleus there are the electrons.
Learn more about the atom at: brainly.com/question/17545314
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