Polonium-214 went through a series of radioactive decays to produce a stable isotope of bismuth-210 choose the correct decay series that would produce bismuth-210 A: Polonium-214 undergoes 2 beta decay and 1 gamma emission
B: Polonium-214 undergoes 1 alpha decay and 2 gamma emission
C: Polonium-214 undergoes 2 alpha decay and 1 beta decay
D: Polonium-214 undergoes 1 alpha decay 1 beta decay and 1 gamma emission.

The correct decay series :

₈₄Po²¹⁴⇒₈₃Bi²¹⁰+₂He⁴+ ₋₁e⁰+ ₀γ⁰

Radioactivity is the process of unstable isotopes to stable isotopes by decay, by emitting certain particles,  

Decay's reaction :

₈₄Po²¹⁴⇒₈₃Bi²¹⁰+x+y+z

From this decay reaction can be concluded

mass number decreased by 4

atomic number decreased by 1

Then the most suitable are:

Polonium-214 undergoes 1 alpha decay 1 beta decay and 1 gamma emission.

₈₄Po²¹⁴⇒₈₃Bi²¹⁰+₂He⁴+ ₋₁e⁰+ ₀γ⁰

So that the mass number and atomic number are the same both before and after decay