Correct option is (C) Nearly 0.8 × 106 eV
When e– has zero kinetic energy total energy is shared by antineutrino and proton. This time energy of antineutrino is its maximum possible kinetic energy. As antineutrino is very light mass in comparison to proton so it will have almost contribution in total energy.
∴ Its energy is almost 0.8 × 106 eV.