In Addition to Charge and Baryon Number, Another Conserved Quantity $\mathrm{X}$

In addition to charge and baryon number, another conserved quantity in particle interactions is lepton number. The six leptons have lepton number +1 , and their antiparticles have lepton number -1 . The lepton numbers for each generation (electron, muon, tau) are separately conserved. For example, an electron has electron-lepton number +1 , while the electron antineutrino has electron-lepton number -1 . What is the missing particle $\mathrm{X}$ in the following reaction? $\rightarrow \overline{\mathrm{n}}+\mathrm{X}$

A) $\tau$
B) $\pi^{-}$
C) $\mathrm{e}^{-}$
D) $\mu^{-}$
E) $\bar{p}$