Answer + brainliest what element undergoes alpha decay to form lead-208?

The three naturally-occurring actinide alpha decay chains given below—thorium, uranium/radium (from U-238), and actinium (from U-235)—each ends with its own specific lead isotope (Pb-208, Pb-206, and Pb-207 respectively).

That would be pollonium 212 because an alpha particle has a mass number of 4 and contains 2 protons.   212 - 4 = 208  and atomic number goes from 84 to 82.

It’s the energy source of stars