Answer:
The correct answer to the question is
d. the nucleus is decaying
Explanation:
A radioactive isotope are variations of of a chemical element with different molecular mass and an unstable nucleus that emit alpha, beta or gamma radiation. An isotope releasing an alpha particle during nuclear decay, releases two neutrons and two protons which make up the alpha particle. If an beta particle is released, then a negative charge equivalent to an electron is released from the nucleus during disintegration. Both forms of nuclear decay results in the release of Gamma radiation.
ome isotopes release an alpha particle during nuclear disintegration; an alpha particle consists of two protons and two neutrons (equivalent to the nucleus of an atom of helium). Others release a beta particle, which is an electron, or negatively charged nuclear particle. Beta particles originate in the nucleus, presumably by breakdown of a neutron into its proton-electron components. Gamma rays are released during both types of radioactive decay.