A polonium nucleus, $^{{214}}_{{84}}\mathrm{Po}$, undergoes decay by releasing an $\alpha$-particle, so that it changes into a lead nucleus. This lead nucleus is also unstable. It then decays by releasing a $\beta^{-}$ particle to create a bismuth nucleus, which afterwards decays by releasing a $\beta^{-}$ particle and forms a nucleus X. How many neutrons are present in nucleus X?
- A126
- B128
- C130
- D210