In β-decay, an electron comes out from an atom. The electron comes out due to nuclear change, not fr — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

Step 1 - The β⁻ Decay Nuclear Reaction In β⁻ decay, a neutron inside the nucleus spontaneously converts into a proton, emitting a high-speed electron (the β⁻ particle) and an electron antineutrino directly from the nucleus: $$\ce{^1_0n -> ^1_1p + ^0_{-1}e + \bar{\nu}_e}$$ Key nuclear changes per β⁻ decay: - Mass number $A$: **unchanged** (total nucleons conserved: one neutron becomes one proton) - Atomic number $Z$: **increases by 1** (one extra proton in the nucleus) Step 2 - Why the Atomic Species Must Change Atomic identity (the atomic species) of an element is uniquely defined by its atomic number $Z$. Since β⁻ decay increases $Z$ by 1, the atom transmutes into the next element in the periodic table. Example: $$\ce{^{14}_6C -> ^{14}_7N + ^0_{-1}e + \bar{\nu}_e}$$ Carbon ($Z = 6$) → Nitrogen ($Z = 7$): a completely different atomic species. Contrast this with orbital ionization: stripping an electron from an orbit leaves the nucleus untouched ($Z$ unchanged), so the atomic species stays the same. The fact that β decay changes the atomic species is the direct proof that the electron was born inside the nucleus — not stripped from an orbit. Step 3 - Analysis of Each Option - **(A) the atomic number increases by one unit** — True, but this is the underlying nuclear cause, not itself the distinguishing proof that the electron came from the nucleus rather than from an orbit. - **(B) the mass number remains unchanged** — True, but orbital ionization also leaves $A$ unchanged, so this cannot distinguish between the two processes. - **(C) the atomic species get changed** — **Correct.** Only a nuclear process changes $Z$, and hence the element's identity. This change in atomic species is the definitive proof of the nuclear origin of the emitted electron. - **(D) the atomic species remains unchanged** — Incorrect. Since $Z$ increases by 1, the element must change. $$\boxed{\text{Answer: C}}$$