Final answer:
Among the given choices, the molecule predicted to be diamagnetic is N2 because it has all of its electrons paired and no unpaired electrons, which is the defining characteristic of a diamagnetic substance.
Step-by-step explanation:
To determine which of the molecules or ions would be predicted to be diamagnetic, we need to look at the electronic configuration and the presence of unpaired electrons. A diamagnetic species has all of its electrons paired and shows no net magnetic field when exposed to an external magnetic field.
- He2-: This species is not actually stable or commonly observed, and the He2+ ion would likely have all electrons paired, but as written as He2- it would predictably have an unpaired electron, making it paramagnetic.
- N2: Nitrogen gas has a triple bond with each nitrogen having its electrons paired off, making it diamagnetic.
- F2-: The addition of an electron to the F2 molecule would result in one unpaired electron, making F2- paramagnetic.
- B2: Boron has a single electron in a p-orbital in its atomic state, and in diatomic B2, there would be two unpaired electrons, one from each boron atom, making B2 paramagnetic.
Therefore, the molecule predicted to be diamagnetic among the choices given is N2. All the other options listed would have unpaired electrons and would be paramagnetic.