No, a proton and a neutron cannot directly combine to form another proton. A proton and a neutron are both baryons, which are composite particles made up of quarks. A proton is composed of two up quarks and one down quark, while a neutron consists of two down quarks and one up quark. They have different quark compositions, resulting in different electric charges.
During certain nuclear reactions, such as nuclear decay or nuclear fusion/fission processes, protons and neutrons can interact and change their respective states. For example, in beta decay, a neutron can undergo a process where it is transformed into a proton, emitting an electron and an electron antineutrino.
In nuclear fusion processes, protons can combine to form heavier atomic nuclei, such as the fusion of two protons to form a deuterium nucleus. However, this process involves other fundamental particles and intermediate steps, and it does not result in the direct conversion of a proton and a neutron into another proton.
In summary, a proton and a neutron cannot simply combine to form another proton. The interaction and transformation of protons and neutrons involve more complex processes such as nuclear reactions or particle interactions.