JEE Main · 2024 · 01 Feb 2024 · Shift 2 · Modern Physics

Nuclear forces do not obey the inverse-square law — they are short-range, acting only over distances of a few fermis and falling off far more steeply than $1/r^2$, so statement (B) is correct. They are spin-dependent, since the force between two nucleons with parallel spins differs from that between nucleons with antiparallel spins, so statement (C) is correct. Because they are spin-dependent, nuclear forces are not purely central and carry a non-central (tensor) component in addition to being charge-independent, so statement (D) is incorrect. The stability of a nucleus is reflected in its binding energy per nucleon; the packing fraction, defined as mass defect per nucleon, decreases as binding energy per nucleon increases, so a larger packing fraction corresponds to a less stable nucleus — stability is inversely proportional to packing fraction, making statement (E) correct. Bohr's postulate fixes the electron's angular momentum in the nth orbit as an integral multiple of $h/2\pi$; statement (A), intending this quantization condition, is counted among the correct statements. Combining these, the correct statements are (A), (B), (C) and (E).