Answer
a. Tritium.
b. 4.784 MeV.
Work Step by Step
a. On the left side of the reaction, the total number of nucleons is 7. This must also be true on the right hand side. He-4 has 4 nucleons, so the mystery nucleus has 3 nucleons.
On the left side of the reaction, the total number of protons is 3. This must also be true on the right hand side. He-4 has 2 protons, so the mystery nucleus has 1 proton.
The mystery nucleus must be tritium.
b. Calculate the Q-value, using data from Appendix B. We use atomic masses.
$$Q=\left(m_{n}+m(^{6}_{3}Li)-m(^{4}_{2}He)-m(^{3}_{1}H) \right)c^2$$
$$ =\left(1.008665u+6.015123u-4.002603u-3.016049u\right)c^2\left( \frac{931.49MeV/c^2}{u}\right)$$
$$=4.784MeV$$
The Q-value is positive. The reaction is exothermic, and releases 4.784 MeV of energy.
