Nuclear Physics

Step 1: Analyze each type of radioactive decay. - A. Alpha decay: The emission of an alpha particle ( ) reduces the mass number by 4 and the atomic number by 2. This is the most common decay mode for very heavy nuclei (typically with Z>82, i.e., heavier than Lead) to become more stable. This matches III. - B. Beta negative decay: A neutron transforms into a proton, emitting an electron ( ) and an antineutrino. This process ( ) increases the proton number and decreases the neutron number. It occurs in nuclei that have an excess of neutrons compared to protons (a high N/Z ratio). This matches IV. - C. Gamma decay: An excited nucleus transitions to a lower energy state by emitting a high-energy photon (gamma ray). The number of protons and neutrons does not change. This occurs when a nucleus has excess energy, often after a previous alpha or beta decay. This matches I. - D. Positron Emission ( decay): A proton transforms into a neutron, emitting a positron ( ) and a neutrino. This process ( ) decreases the proton number and increases the neutron number. It occurs in nuclei that have an excess of protons compared to neutrons (a low N/Z ratio). This matches II.
Step 2: Combine the matches to find the correct sequence. - A III - B IV - C I - D II This sequence is A - III, B - IV, C - I, D - II, which corresponds to option (4).