α-particle is considered identical to He-nucleus because — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

Step 1 - Composition of Alpha Particle An $\alpha$-particle consists of 2 protons + 2 neutrons, identical to $\ce{^4_2He^{2+}}$ (helium-4 nucleus). Step 2 - Rutherford-Royds Experiment (1909) Rutherford and Royds placed radon-222 (an $\alpha$-emitter) in a thin-walled glass tube inside an evacuated sealed outer vessel. Alpha particles penetrated the thin walls and captured electrons: $$\ce{He^{2+} + 2e^- -> He(g)}$$ Spectroscopic analysis of the accumulated gas showed the characteristic helium emission spectrum, directly proving that $\alpha$-particles are helium nuclei. Step 3 - Option Analysis - (A) Incorrect: He nuclei are not pre-formed inside the parent nucleus. - (B) Incorrect: Stating composition is not experimental proof. - (C) Correct: He gas accumulation in sealed vessel with $\alpha$-emitter = direct proof. - (D) Incorrect: He-4 is stable but not the most stable nucleus (Fe-56 has highest BE/nucleon). $$\boxed{C}$$