Q135 / 200 · NEET 2010 (Screening) · Physics
The mass of a ${ }_3 \mathrm{Li}^7$ nucleus is $0.042 \mathrm{u}$ less than the sum of the masses of all its nucleons. The binding energy per nucleon of ${ }_3 \mathrm{Li}^7$ nucleus is nearly
- A$46 \mathrm{MeV}$
- Correct answerB$5.6 \mathrm{MeV}$
- C$3.9 \mathrm{MeV}$
- D$23 \mathrm{MeV}$
Solution
If $\mathrm{m}=1 \mathrm{u}, \mathrm{c}=3 \times 10^8 \mathrm{~ms}^{-1}$, then $\mathrm{E}=931 \mathrm{MeV}$ ie, $1 \mathrm{u}=931 \mathrm{MeV}$ Binding energy $=0.042 \times 931=39.10 \mathrm{MeV}$ $\therefore$ Binding energy per nucleon
$$
=\frac{39.10}{7}=5.58 \approx 5.6 \mathrm{MeV}
$$
Hence, the correct answer is option: 'B'.