${}_{90}{}^{232}\mathrm{Th}$  an isotope of thorium decays in ten stages emitting six $\mathrm{\alpha }$-particles and four $\mathrm{\beta }$-particles in all. The end product of the decay is

• A

  ${}_{90}{}^{232}\mathrm{Th}$

• B

  ${}_{82}{}^{ 206}\mathrm{Pb}$

• C

  ${}_{82}{}^{ 209}\mathrm{Pb}$

• D

  ${}_{82}{}^{ 208}\mathrm{Pb}$