Given the masses of various atomic particles
m_p = 1.0072 u, m_n = 1.0087 u, m_e = 0.000548 u,
${m_{\overline v }}$ = 0, m_d = 2.0141 u, where p $\equiv$ proton, n $\equiv$ neutron,
e $\equiv$ electron, $\overline v$ $\equiv$ antineutrino and d $\equiv$ deuteron. Which of the following process is allowed by momentum and energy conservation?

1. A n + n $\to$ deuterium atom <br>(electron bound to the nucleus)
2. B n + p $\to$ d + $\gamma$ Correct answer
3. C p $\to$ n + e⁺ + $\overline v$
4. D e⁺ + e^- $\to$ $\gamma$