| Q: | Alpha decay most commonly takes place in atoms with a large proton to neutron ratio. Which of the following atoms has the lowest proton to neutron ratio? |
| A | | Po-209 |
| B | | Po-210 |
| C | | Pb-210 |
| D | | Pb-209 |
The correct answer is C. Po is polonium and Pb is lead. The number following is atomic wieght, which is the sum of the protons and neutrons (electrons have negligible weight in this case). We can eliminate the -209 answer choices right away since they have one less neutron than the -210 choices, and thus have a higher proton-neutron ratio. The increase in weight is due to an increased number of neutrons, not protons. To choose between B and C, we have to remember which element comes first on the periodic table, which in this case is lead, Pb. Pb-210 has 82 protons and 128 neutrons. Po-210 has 84 protons and 126 neutrons.