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

option B

Explanation:

The question is incomplete. Here is the complete question.

The atomic symbol 206 82 Pb 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?

A. 238 92 U

B. 222 87 Pb

C. 178 72 Hf

D. 192 77 Pb

Let's talk about isotopes first. Isotopes are atoms of the same element with identical number of protons but different number of neutrons. For e. g. Pb 206 and Pb-208 are isotopes. Both have same number of protons i. e. 82. However, Pb-206 has 124 neutrons while Pb 208 has 126 neutrons.

Radioactive decay happens when either alpha particle (atomic mass = 4, atomic number=2), beta particle (an electron) or gamma rays are emitted from an atom.

If alpha emits, the atomic mass reduces by 4 and atomic number reduces by 2 If beta emits, atomic number increases by + 1. If gamma emits, no change to the atom occurs.

Now since Pb-206 was made from an isotope, option A and option C rules out. Radioactive decay results in reduction of atomic mass, hence option D is wrong too. Therefore, the correct answer is option B. Below is the equation for the decay.

222,87 Pb → 206,82 Pb + 4 (4,2 He) + 3 (0,-1 e)

To simplify, 4 alpha particles and 3 beta particles were emitted from 222,87Pb to create 206,82 Pb.