(i) Determining the mass and atomic number of ${\mathrm{A}}_4$ and $\mathrm{A}$
(ii) Basic nuclear processes of ${\mathit{\beta }}^{+}$and ${\mathit{\beta }}^{-}$decays
(i) ${\mathrm{A}}_4:$ Mass Number : 172

Atomic Number : 69
A : Mass Number : 180
Atomic Number : 72
[Alternatively : Give full credit if student considers decay and find atomic and mass numbers accordingly
${}_{72}^{180}\mathrm{A}\stackrel{\mathit{\alpha }}{\mathit{─}\mathit{─}▸}{}_{70}^{176}{\mathit{A}}_1\stackrel{{\mathit{\beta }}^{+}}{\mathit{─}\mathit{─}▸}{}_{71}^{176}{\mathit{A}}_2\stackrel{\mathrm{\alpha }}{\mathit{─}\mathit{─}▸}$ ${}_{69}^{172}{\mathit{A}}_3\stackrel{\mathit{\gamma }}{\mathit{─}\mathit{─}▸}{}_{69}^{172}{\mathit{A}}_4$
Gives the values quoted above.
If the student takes ${\mathit{\beta }}^{+}$decay
${}_{72}^{180}\mathrm{A}\stackrel{\mathit{\alpha }}{\mathit{─}\mathit{─}▸}{}_{70}^{176}{\mathit{A}}_1\stackrel{{\mathit{\beta }}^{+}}{\mathit{─}\mathit{─}▸}{}_{71}^{176}{\mathit{A}}_2\stackrel{\mathrm{\alpha }}{\mathit{─}\mathit{─}▸}$ ${}_{69}^{172}{\mathit{A}}_3\stackrel{\mathit{\gamma }}{\mathit{─}\mathit{─}▸}{}_{69}^{172}{\mathit{A}}_4$
This would give the answers: $\left({\mathrm{A}}_4:172,69\right);\left(\mathrm{A}:180,74\right)]$
(ii) Basic nuclear process for ${\mathit{\beta }}^{+}$decay $\mathit{p}\to \mathit{n}+{}_1^0\mathit{e}$ $+\mathit{v}$
For ${\mathit{\beta }}^{-}$decay $\mathit{n}\to \mathit{p}+{}_{-1}^0\mathit{e}+\overline{\mathit{v}}$
[Note: Give full credit of this part, if student writes the processes as conversion of proton into neutron for decay and neutron into proton for decay.]