What is the particle X in the fusion reaction shown below? \( {}_{1}^{2}\mathrm{H} + {}_{1}^{2}\mathrm{H} \rightarrow {}_{2}^{3}\mathrm{He} + X + 3.27\,\mathrm{MeV} \)
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → a neutron
In every nuclear reaction the mass number (total number of nucleons) and the charge number are conserved. Let X be \( {}_{Z}^{A}X \).
\( \text{Mass number: } 2 + 2 = 3 + A \;\Rightarrow\; A = 1 \)
\( \text{Charge number: } 1 + 1 = 2 + Z \;\Rightarrow\; Z = 0 \)
A particle with \( A = 1 \) and \( Z = 0 \) is a neutron, \( {}_{0}^{1}n \).
NCERT (2026-27):
Nuclear Fusion – Energy Generation in Stars – “… Some examples of such energy liberating nuclear fusion reactions are :
\( \displaystyle {}^{2}_{1}\mathrm{H} + {}^{2}_{1}\mathrm{H} \rightarrow {}^{3}_{2}\mathrm{He} + n + 3.27\ \mathrm{MeV} \qquad [13.13(b)] \)”
Controlled Thermonuclear Fusion – “… However, the number of protons and the number of neutrons are both separately conserved in a nuclear reaction.”