Question

Mass numbers of the elements $A, B, C$ and $D$ are $30, 60, 90$ and $120$ respectively. The specific binding energy of them are $5 \, MeV, 8.5 \, MeV, 8 \, MeV$ and $7 \, MeV$ respectively. Then, in which of the following reaction/s energy is released ? (a) $D \rightarrow 2B$ (b) $C \rightarrow B + A$ (c) $B \rightarrow 2 A$

• A. only in (a)
• B. in (b), (c)
• C. in (a), (c)
• D. in (a), (b) and (c)

Answer 1

Answer: (A)

only in (a)

Answer 2

(1) $\Delta E=2 \times 60 \times 8.5-120 \times 7=180\, MeV$
(2) $\Delta E=60 \times 8.5+30 \times 5-90 \times 8=-60 \,MeV$
(3) $\Delta E=2 \times 30 \times 5-60 \times 8.5=-105 \,MeV$
Hence, energy is released in (1) only.