A large atom decays and emits a particle. After the reaction is complete, the atom’s mass has changed substantially. What kind of particle has most likely been emitted?

An alpha particle contains two protons and two neutrons, so emitting one can noticeably change an atom’s mass and mass number. A beta particle or positron has very little mass, while a photon has no rest mass. Therefore, the most likely particle is an alpha particle.

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