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The nuclear binding energy per nucleon (B/A) versus mass number (A) graph is as shown. A nucleus with mass number A = 110 undergoes fission and splits into two fragments. Which of the following pairs of resulting mass numbers is energetically most favourable (i.e., releases maximum energy)?

1. 80 and 30
2. 60 and 50
3. 100 and 10
4. 90 and 20

Correct answer: 60 and 50

Solution

The B/A curve peaks around A = 56 at approximately 8.8 MeV per nucleon and decreases for both lighter and heavier nuclei. For fission of A=110 (B/A roughly 8.5 MeV), the released energy per nucleon is proportional to (B/A)_products - (B/A)_parent. The pair 60 and 50 both lie near the peak of the curve, giving the highest average B/A for the products and hence the maximum energy release.

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