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Fission of nuclei is possible because the binding energy per nucleon in them -
A
Decreases with mass number at low mass numbers
B
Increases with mass number at low mass numbers
C
Decreases with mass number at high mass numbers
D
Increases with mass number at high mass numbers
Detailed Solution
The binding energy per nucleon rises with mass number for light nuclei, reaches a maximum of about 8.8 MeV near $A = 56$ (iron), and then decreases slowly for heavier nuclei.
For a heavy nucleus such as uranium ($A \approx 235$) the binding energy per nucleon is about 7.6 MeV.
When it splits into two medium-mass nuclei ($A \approx 90$ to 140), the products have a higher binding energy per nucleon, about 8.5 MeV.
The products are more tightly bound, and the difference in binding energy is released as energy.
So fission of heavy nuclei is possible because the binding energy per nucleon decreases with mass number at high mass numbers.
For a heavy nucleus such as uranium ($A \approx 235$) the binding energy per nucleon is about 7.6 MeV.
When it splits into two medium-mass nuclei ($A \approx 90$ to 140), the products have a higher binding energy per nucleon, about 8.5 MeV.
The products are more tightly bound, and the difference in binding energy is released as energy.
So fission of heavy nuclei is possible because the binding energy per nucleon decreases with mass number at high mass numbers.