An atom that has 84 protons and 86 neutrons undergoes a reaction. at the end of the reaction, it has 82 protons and 84 neutrons. what happened to the atom? it accepted radiation in a chemical reaction. it donated neutrons to another atom in a chemical reaction. it emitted an alpha particle in a nuclear reaction. it accepted protons in a nuclear reaction.

It emitted an alpha particle in a nuclear reaction

Explanation:

The initial atom has:

84 protons and 86 neutrons

After the reaction, the atom has

82 protons and 84 neutrons

It means that the atom has lost 2 protons and 2 neutrons. Therefore, the atom has emitted a particle containing 2 protons and 2 neutrons: this corresponds to an alpha particle, which is a nucleus of helium, consisting in fact of 2 protons and 2 neutrons.

The process that took place is called alpha decay.