WAEC Physics 2021 Paper

Concept:Alpha emission is a type of radioactive decay in which the nucleus loses $2$ protons and $2$ neutrons, causing its atomic number to change.Explanation:An $\alpha$-particle is a helium nucleus: $\mathrm{_2^4He}$.When an atom emits an $\alpha$-particle, its mass number decreases by $4$ and its atomic number decreases by $2$.For a parent nucleus ${}_{Z}^{A}\mathrm{X}$, the decay can be written as:$${}_{Z}^{A}\mathrm{X} \rightarrow {}_{Z-2}^{A-4}\mathrm{Y} + {}_2^4\mathrm{He}$$Because the atomic number changes from $Z$ to $Z-2$, the daughter nucleus belongs to a completely different element.So the atom does not merely "may" change; it always changes into a different element.The daughter has decreased mass, not increased mass.It is also not a different isotope, because the identity of the element itself changes.Answer:D. becomes a daughter of a different element always.