Question

The atomic symbol Superscript 206 subscript 82 upper P b. represents lead-206 (Pb-206), an isotope that has 82 protons and 124 neutrons. Which atomic symbol could represent an isotope that undergoes radioactive decay to produce Pb-206?
Superscript 238 subscript 92 upper U.
Superscript 222 Subscript 87 upper P b
Superscript 178 subscript 72 upper H f.
Superscript 192 subscript 77 upper P b.

Answer 1

Superscript 238 subscript 92 U (uranium-238).

Reason: Pb-206 is the stable end product of the U-238 decay series (a sequence of alpha and beta decays). The other options have masses less than 206 or inconsistent element symbols and thus cannot decay to Pb-206.