Answer
The conservation of baryon number would be violated.
Work Step by Step
A proton has a lepton number of $0$
Electrons and neutrinos each have a lepton number of $1$
Their antiparticles each have a lepton number of $-1$
Therefore, the conservation of lepton number would not be violated.
A proton has a baryon number of $1$
Electrons, neutrinos, and their antiparticles each have a baryon number of $0$
Therefore, the conservation of baryon number would be violated.
