Since an electron and an antineutrino are emitted from a pure beta-active material, these particles do not have same energy due to their different masses. The beta particles are ejected when a neutron is converted into a proton and thus we can’t say that beta particles were already present in the nucleus. The mass of antineutrino is unknown. Hence, Option A, B and C are not correct. Nuclei with same mass number but different atomic number are called isobars. The beta decay process is. It is prevalent that, (Before beta decay) while (after beta decay). Thus we say that the active nucleus changes to one of its isobars after the beta decay.