Final answer:
Nuclides that are most likely to decay by beta decay have an imbalanced neutron-to-proton ratio, with high neutron-to-proton ratios leading to beta minus decay and low ratios leading to positron emission.
Step-by-step explanation:
Nuclides most likely to undergo beta decay are those with imbalanced neutron-to-proton ratios, typically with a higher ratio of neutrons to protons. Beta decay occurs in two major forms: beta minus (β-) decay and beta plus (β+) decay, also known as positron emission. In β- decay, a neutron is converted into a proton with the emission of an electron (β particle) and an antineutrino, leading to an increase in the atomic number. In positron emission, a proton is converted into a neutron, emitting a positron (the antiparticle of the electron) and a neutrino, which results in a decrease in the atomic number.
For instance, nuclides with high neutron-to-proton ratios, especially those with atomic numbers less than 83, are candidates for β- decay to achieve greater stability. Conversely, nuclides with low neutron-to-proton ratios may undergo positron emission or electron capture to improve their stability by decreasing their atomic number. Massive nuclides, with atomic numbers greater than 83, tend to decay via alpha emission or spontaneous fission rather than beta decay.