Step 1: The binding energy per nucleon varies with mass number.
Step 2: The curve shows that lighter nuclei and very heavy nuclei have lower binding energy, while medium-sized nuclei (e.g., iron) have the highest binding energy, making them more stable. \[ \boxed{\text{Most stable nucleus: } \text{Fe (A = 56)}} \]
(i) Nuclear Fission
Solution:
Nuclear fission is the process where a heavy nucleus splits into smaller nuclei, releasing energy.
Step 1: Heavy elements such as uranium-235 split into lighter elements when bombarded with neutrons.
Step 2: This process releases energy due to the increase in binding energy per nucleon. \[ \boxed{\text{Heavy nucleus } \rightarrow \text{ Two lighter nuclei } + \text{ Energy}} \]
(ii) Nuclear Fusion
Solution: Nuclear fusion is the process where lighter nuclei combine to form a heavier nucleus, releasing energy.
Step 1: Light elements such as hydrogen nuclei fuse together under high temperature and pressure to form helium.
Step 2: This results in a release of energy due to an increase in binding energy per nucleon. \[ \boxed{\text{Light nuclei } \rightarrow \text{ Heavier nucleus } + \text{ Energy}} \]
(iii) Nuclear Energy
Solution: Nuclear energy is the energy released during fission or fusion due to changes in binding energy.
Step 1: The energy released during fission and fusion reactions is calculated using Einstein's equation: \[ E = mc^2 \] Step 2: This energy is harnessed in nuclear reactors and stars. \[ \boxed{\text{Energy is released due to mass defect.}} \]
Mention the events related to the following historical dates:
\[\begin{array}{rl} \bullet & 321 \,\text{B.C.} \\ \bullet & 1829 \,\text{A.D.} \\ \bullet & 973 \,\text{A.D.} \\ \bullet & 1336 \,\text{A.D.} \\ \bullet & 1605 \,\text{A.D.} \\ \bullet & 1875 \,\text{A.D.} \\ \bullet & 1885 \,\text{A.D.} \\ \bullet & 1907 \,\text{A.D.} \\ \bullet & 1942 \,\text{A.D.} \\ \bullet & 1935 \,\text{A.D.} \end{array}\]