In the nuclear reaction \( \mathrm{X}+{}^{1}_{0}\mathrm{n}\rightarrow{}^{4}_{2}\mathrm{He}+{}^{7}_{3}\mathrm{Li} \), which of the following is the nucleus X?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( {}^{10}_{5}\mathrm{B} \)
In a nuclear reaction, the number of protons and the number of neutrons are each conserved. So the mass numbers (upper indices) and the atomic numbers (lower indices) add up to the same totals on the two sides. Let the nucleus be \( {}^{A}_{Z}\mathrm{X} \).
The mass numbers give:
\( A+1=4+7 \)
\( \Rightarrow\; A=10 \)
The atomic numbers give:
\( Z+0=2+3 \)
\( \Rightarrow\; Z=5 \)
The element with \( Z=5 \) is boron. Therefore, X is \( {}^{10}_{5}\mathrm{B} \).
NCERT (2026-27):
Example 13.4 – “… In a nuclear reaction, elements may be transmuted. Thus, the number of atoms of each element is not necessarily conserved in a nuclear reaction. However, the number of protons and the number of neutrons are both separately conserved in a nuclear reaction.”