Which of the following statements are correct?
(A) For a pair of nucleons, the force is attractive for distances larger than 0.8 fm.
(B) The density of a nucleus is dependent of A.
(C) Nuclides with same neutron number but different atomic number are called isotones.
(D) \( \beta^{+} \) decay process is the conversion of neutron to proton.
(E) Plutonium undergoes fission with slow neutrons.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (C) and (E) Only
(A) For a pair of nucleons, the force is attractive for distances larger than 0.8 fm. — Correct. The potential energy of a pair of nucleons is a minimum at about 0.8 fm, so the nuclear force is attractive beyond that distance and repulsive below it.
(B) The density of a nucleus is dependent of A. — Incorrect. The volume and the mass are both proportional to A, so the density is the same for all nuclei.
(C) Nuclides with same neutron number but different atomic number are called isotones. — Correct. For example \( {}_{80}^{198}\mathrm{Hg} \) and \( {}_{79}^{197}\mathrm{Au} \) have the same number of neutrons.
(D) \( \beta^{+} \) decay process is the conversion of neutron to proton. — Incorrect. In \( \beta^{+} \) decay a proton changes into a neutron, with the emission of a positron and a neutrino.
(E) Plutonium undergoes fission with slow neutrons. — Correct. Plutonium formed from uranium-238 in a reactor can itself undergo fission under bombardment by slow neutrons.
Note: Statements (A), (B) and (C) of this question are from the latest textbook (2026-27). Statement (E), that plutonium undergoes fission with slow neutrons, is printed only in the pre-rationalised textbook (2022-23). It was removed from the latest book, and it also appears to be out of the CUET 2026 syllabus.
NCERT (2026-27):
Nuclear Force – “… The potential energy is a minimum at a distance r0 of about 0.8 fm. This means that the force is attractive for distances larger than 0.8 fm and repulsive if they are separated by distances less than 0.8 fm.”
Size of the Nucleus – “… Thus the density of nucleus is a constant, independent of A, for all nuclei.”
Atomic Masses and Composition of Nucleus – “… Nuclides with same neutron number N but different atomic number Z, for example 19880Hg and 19779Au, are called isotones.”
NCERT (Pre-rationalised edition, 2022-23):
Nuclear Reactor – “… Plutonium is highly radioactive and can also undergo fission under bombardment by slow neutrons.”