Question

a large atom decays and emits a particle. after the reaction is complete, the atoms mass has changed substantially. what kind of particle has most likely been emitted? alpha particle beta particle positron photon

Explanation:

An alpha - particle consists of 2 protons and 2 neutrons. When an atom emits an alpha - particle, its mass number decreases by 4 and atomic number decreases by 2, resulting in a substantial mass change. A beta - particle (electron or positron) has a very small mass compared to a proton or neutron, and a photon has no mass. So, an alpha - particle emission causes the most significant mass change for the atom.

Answer:

alpha particle