(a) Binding Energy per Nucleon Curve and Significance

Step 1 (Graph Representation): [1 Mark]

The variation of binding energy per nucleon ($BE/A$) with mass number ($A$) is represented by a graph where the $y$-axis is $BE/A$ (in MeV) and the $x$-axis is the mass number $A$. The curve rises sharply for light nuclei, reaches a maximum of about $8.8 \text{ MeV}$ for $A \approx 56$ (Iron), and then gradually decreases for heavier nuclei.

Step 2 (Significance): [0.5 Mark]

• The curve explains the stability of nuclei: nuclei with higher $BE/A$ are more stable.
• It explains the phenomenon of nuclear fission (heavy nuclei splitting) and nuclear fusion (light nuclei joining) to achieve a more stable state.

(b) Analysis of Nuclear Reaction

Step 1 (Identification): [0.5 Mark]

(i) Since two lighter nuclei combine to form a heavier nucleus with higher binding energy per nucleon, this process is known as Nuclear Fusion.

Step 2 (Mass Defect Analysis): [0.5 Mark]

(ii) According to the mass-energy equivalence principle, if the product nucleus is more stable (higher $BE/A$), it must have a lower mass per nucleon. Therefore, the total mass of the product nucleus is less than the sum of the masses of the initial nuclei. The difference is released as energy ($Q = \Delta m c^2$).

Step 3 (Energy Consideration): [0.5 Mark]

(iii) The process produces energy (exothermic). Because the final system is in a lower potential energy state (more stable), the excess mass is converted into kinetic energy of the products and radiation.