Q 12-13-101JEE MainJEE Main 2021 (18 Mar, Shift 2)Easy
The decay of a proton to neutron is:
Answer: (B) possible only inside the nucleus
A free proton cannot decay into a neutron because the neutron is heavier. Inside a nucleus the extra energy can come from the binding energy, so $p \to n + e^+ + \nu$ ($\beta^+$ decay) happens only inside nuclei.
Solution by Sreeraj P, M.Sc Physics