Which are the three major modes of radioactive decay?

• A. Alpha particle emission; Beta particle emission; Gamma ray emission
• B. Alpha, Neutron, Gamma
• C. Proton emission
• D. Electron capture only

Answer: (A)

The main idea is identifying the three principal ways a radioactive nucleus can shed energy and change its state: alpha decay, beta decay, and gamma decay. In alpha decay, the nucleus emits an alpha particle (two protons and two neutrons), which lowers the atomic number by 2 and the mass number by 4. In beta decay, a neutron can convert to a proton with the emission of a beta particle (an electron) and an antineutrino, raising the atomic number by 1 (or a proton can convert to a neutron with a positron and a neutrino, lowering the atomic number by 1), while the mass number stays the same. Gamma decay involves emitting a gamma ray, a high-energy photon, from an excited nucleus; this lowers the nucleus’s energy but leaves its proton and mass numbers unchanged. The combination of alpha, beta, and gamma emissions is the standard trio that encompasses the main decay pathways. The other options point to less general or rarer processes (like neutron or proton emission or electron capture-only scenarios) and don’t represent the common, broad classification of radioactive decay modes.