c) Simon:
²²⁵Ra (β⁻, t½ = 14.9 d) →
²²⁵Ac (α, t½ = 9.92 d) →
²²¹Fr (α, t½ = 4.18 min) →
²¹⁷At (α, t½ = 32.3 ms) →
²¹³Bi (β⁻, t½ = 45.6 min) →
²¹³Po (α, t½ = 3.65 μs) →
²⁰⁹Pb (β⁻, t½ = 3.25 h) →
²⁰⁹Bi (α, t½ = 2.01 × 10¹⁹ y) (this is WAY more than the age of the universe so it’s unlikely that any atom in the sample will become tellurium in Simon’s lifetime)→
²⁰⁵Tl (stable)