which element would most likely have an electron affinity measuring closest to zero?\nna\nal\nrb\nar

Explanation:

Step1: Recall electron - affinity concept

Electron affinity is the energy change when an electron is added to a gaseous atom. Noble gases have very stable electron configurations with a full outer shell.

Step2: Analyze each element

Na (sodium), Al (aluminum), and Rb (rubidium) are metals and tend to lose electrons rather than gain them easily, but they still have non - zero electron affinities as they can gain an electron to form an anion. Ar (argon) is a noble gas with a stable 8 - electron outer shell ($1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}$). Adding an electron to Ar would require putting the electron in a new, higher - energy shell, which is highly unfavorable energetically. So, its electron affinity is closest to zero.

Answer:

Ar