Two neutral argon-40 atoms, R and S, in a gas-discharge tube each undergo a change involving electrons.
| Atom | Observation |
|---|---|
| R | Electromagnetic radiation is emitted and the final relative charge is 0 |
| S | The final relative charge is +2 |
Which describes the changes involving electrons and compares the final mass numbers?
R: an electron moves to an orbit closer to the nucleus; S: two electrons move to orbits farther from the nucleus; the mass number of S has fallen below 40.
R: an electron moves to an orbit farther from the nucleus; S: two electrons move to orbits farther from the nucleus; both mass numbers are still 40.
R: an electron moves to an orbit closer to the nucleus; S: two outer electrons are lost; both mass numbers are still 40.
R: an electron moves to an orbit farther from the nucleus; S: two outer electrons are lost; the mass number of S has fallen below 40.