0
A baryon always had three quarks. If it hasn't, then it is not a baryon.
It is -1 as it the opposite of the baryon number of a proton.
Baryon
A baryon number is a quantum number related to the difference between the numbers of quarks and antiquarks in a system of subatomic particles.
A baryon acoustic oscillation is one of the regular periodic fluctuations in the density of the visible baryonic matter of the universe.