(i) Determining the mass and atomic number of $A_4$ and $A$ (ii) Basic nuclear processes of $β^{+}$and $β^{-}$decays (i) $A_4:$ 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 $\; {}_{72}^{180} A \xrightarrow[]{ \alpha } {}_{70}^{176} A_1 \xrightarrow[]{ \beta^+ } \; {}_{71}^{176} A_2 \xrightarrow[]{ \alpha }$ $\; {}_{69}^{172} A_3 \xrightarrow[]{ \gamma } \; {}_{69}^{172} A_4$ Gives the values quoted above. If the student takes $β^{+}$decay $\; {}_{72}^{180} A \xrightarrow[]{\alpha} {}_{70}^{176} A_1 \xrightarrow[]{\beta^{+}} \; {}_{71}^{176} A_2 \xrightarrow[]{\alpha}$ $\; {}_{69}^{172} A_3 \xrightarrow[]{\gamma} \; {}_{69}^{172} A_4$ This would give the answers: $( A_4: 172,69) ;( A: 180,74)]$ (ii) Basic nuclear process for $β^{+}$decay $p \rightarrow n + {}_{1}^{0} e$ $+v$ For $β^{-}$decay $n \rightarrow p + {}_{-1}^{0} e + \overline{v}$ [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.]