To determine the number of neutrons in the atom after the emission of a β-particle and an α-particle from ‌83214‌Bi, we need to understand how these emissions affect the atomic and mass numbers. 1. Emission of a β-particle: Aβ-particle is essentially an electron, and its emission converts a neutron into a proton. Therefore, the atomic number increases by 1 , but the mass number remains the same. For ‌83214‌Bi (bismuth), after the emission of a β-particle, the atomic number becomes 84 : ‌83214‌Bi⟶‌84214‌Po+β 2. Emission of an α-particle: An α-particle consists of 2 protons and 2 neutrons, so its emission decreases the atomic number by 2 and the mass number by 4 . Therefore, for ‌84214‌Po (polonium), after the emission of an α-particle, the atomic number becomes 82 and the mass number becomes 210: ‌84214‌Po⟶‌82210‌Pb+α
Now, we need to find the number of neutrons in the resulting atom, ‌82210‌Pb (lead). The number of neutrons is given by the difference between the mass number and the atomic number: Number of neutrons = Mass number - Atomic number Number of neutrons =210−82=128 Therefore, the correct answer is: Option B 128