B. An atom whose nucleus is unstable and emits particles and and energy. This is a Radioactive isotope.
The atomic nuclei of constituent atoms of the same element include the same number of protons but different numbers of neutrons. Radio isotopes are an element's radioactive isotopes. They can alternatively be described as atoms with an excess of energy in their nucleus or atoms with an unstable ratio of neutrons to protons. A radioisotope's unstable nucleus can form either spontaneously or as a result of a deliberate alteration of the atom. Radioisotope production can occur using either a cyclotron or a nuclear reactor. Molybdenum-99, which has a high neutron content, can be produced most effectively in nuclear reactors, whereas fluorine-18, which has a high proton content, can be produced most effectively in cyclotrons. Uranium is the most well-known illustration of a radioisotope that is found naturally. Uranium-238 constitutes all naturally occurring uranium with the exception of 0.7%.
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