Final answer:
The types of radiation emitted by radioactive nuclei are a) alpha, beta, and gamma rays, with alpha particles being equivalent to helium nuclei, beta particles as electrons or positrons, and gamma rays as high-energy photons.
Step-by-step explanation:
The types of radiation emitted by the nuclei of radioactive elements are alpha rays, beta rays, and gamma rays. Alpha particles consist of two protons and two neutrons, which is equivalent to a helium nucleus.
Beta particles can be either electrons or positrons emitted by the nucleus. Gamma rays are high-energy photons. The complete list of radioactive emissions also includes neutrons and positrons, but for the scope of this question and in most common contexts, the primary types of radiation considered are alpha, beta, and gamma.
Therefore, the answer to the question is (a) Alpha, Beta, Gamma.