A nucleus captures two neutrons. Which of the following gives the changes in the proton number and nucleon number of the nucleus?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Proton number: No change; Nucleon number: Increases by 2
The proton number Z is the number of protons, that is, the nuclear charge. A neutron carries no charge, so capturing neutrons adds no proton and Z is unchanged.
The nucleon number A is the total of protons and neutrons. Each captured neutron adds one nucleon, so two neutrons raise A by 2.
\( {}^{A}_{Z}\mathrm{X} + 2\,{}^{1}_{0}\mathrm{n} \rightarrow {}^{A+2}_{Z}\mathrm{X} \)
NCERT (2026-27):
Atomic Masses and Composition of Nucleus – “… The composition of a nucleus can now be described using the following terms and symbols: Z - atomic number = number of protons [13.4(a)] N - neutron number = number of neutrons [13.4(b)] A - mass number = Z + N = total number of protons and neutrons [13.4(c)] One also uses the term nucleon for a proton or a neutron.”