Final answer:
The pairs Mg2+ & Ar and N3- & P3- are isoelectronic because they have the same electron configurations as the noble gases Ne and Ar respectively.
Step-by-step explanation:
Atoms and ions that have the same electron configuration are said to be isoelectronic. To determine which pairs are isoelectronic, we need to compare their electron configurations.
- Mg2+ has an electron configuration similar to Ne because it has lost two electrons (1s2 2s2 2p6).
- Ar naturally has the same electron configuration as Ne (1s2 2s2 2p6).
- N3- has gained three electrons to also have an electron configuration similar to Ne (1s2 2s2 2p6).
- P3- has an electron configuration similar to Ar (1s2 2s2 2p6 3s2 3p6).
- Both As and As3+ cannot be isoelectronic since the ion has lost three electrons.
Therefore, the pairs Mg2+ and Ar, as well as N3- and P3-, are isoelectronic because they share the same electron configurations as the noble gases Ne and Ar respectively.