Read the following passage and answer the questions.
A nucleus is written as \({}^{A}_{Z}\mathrm{X}\), where X is the chemical symbol of the element. Here Z is the atomic number and A is the mass number. The nucleus contains Z protons and (A − Z) neutrons. Protons and neutrons are together called nucleons. For example, the aluminium nucleus \({}^{27}_{13}\mathrm{Al}\) has 13 protons and 14 neutrons. Experiments show that a nucleus of mass number A has a radius \(R=R_0A^{1/3}\), where \(R_0=1.2\ \mathrm{fm}\) and 1 fm = \(10^{-15}\ \mathrm{m}\). The protons in a nucleus are positively charged, so they repel each other. Still, the nucleus does not fly apart. The nucleons are held together by a force of a different kind, called the nuclear force. A rough graph of the potential energy of a pair of nucleons against their separation r has a minimum at a separation \(r_0\) of about 0.8 fm.
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): In the \({}^{27}_{13}\mathrm{Al}\) nucleus, the nuclear force between two protons is about the same as the nuclear force between two neutrons.
Reason (R): The nuclear force between two nucleons depends on their electric charge.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) is correct but (R) is not correct.
Assertion (A) In the \( {}^{27}_{13}\mathrm{Al} \) nucleus, the nuclear force between two protons is about the same as the nuclear force between two neutrons. — True. The nuclear force between two neutrons, between a proton and a neutron, and between two protons is about the same. So a proton pair and a neutron pair in this nucleus feel nearly equal nuclear forces.
Reason (R) The nuclear force between two nucleons depends on their electric charge. — False. The nuclear force does not depend on charge. It is the Coulomb force that depends on charge; it acts between two protons but not between two neutrons.
NCERT (2026-27):
Nuclear Force – “(iii) The nuclear force between neutron-neutron, proton-neutron and proton-proton is approximately the same. The nuclear force does not depend on the electric charge.”