The atomic mass unit (1u) is correctly represented by:

The correct answer is Option (2) → \( 1\,\mathrm{u} = 931.5\,\mathrm{MeV}/c^{2} \)

The atomic mass unit is one-twelfth of the mass of a \( {}^{12}\mathrm{C} \) atom, \( 1\,\mathrm{u} = 1.66\times10^{-27}\,\mathrm{kg} \). By mass-energy equivalence \( E = mc^{2} \), this mass is equivalent to 931.5 MeV of energy, so a mass can also be written as an energy divided by \( c^{2} \).

    \( \displaystyle E = (1.66\times10^{-27}\,\mathrm{kg})(3\times10^{8}\,\mathrm{m\,s^{-1}})^{2} = 1.49\times10^{-10}\,\mathrm{J} \)

    \( \displaystyle \frac{1.49\times10^{-10}\,\mathrm{J}}{1.6\times10^{-13}\,\mathrm{J/MeV}} \approx 931.5\,\mathrm{MeV} \)

So \( 1\,\mathrm{u} = 931.5\,\mathrm{MeV}/c^{2} \).

NCERT (2026-27):
Nuclear Binding Energy – “… Example 13.3 Find the energy equivalent of one atomic mass unit, first in Joules and then in MeV. … Solution 1u = 1.6605 × 10^–27 kg … = 0.9315 × 10⁹ eV = 931.5 MeV or, 1u = 931.5 MeV/c²”