Rank the following elements by electron affinity 1) fluorine 2) selenium 3) arsenic 4) potassum 5) argon

Fluorine > Selenium > Arsenic > Potassium > Argon

Explanation:

Electron affinity describes the ability or readiness or tendency of an atom to gain an electron.

The higher the value, the higher the tendency. Electron affinity depends on the on the nuclear charge and atomic radius. When nuclear charge is more, electron affinity is high, when atomic radius increases electron affinity reduces.

Noble gases such as Helium, Neon, and Argon would have 0 affinity for electrons because of their stable electronic configuration. From the list, Ar is the least in terms of electron affinity.

Potassium is a metal with large electropositivity which describes the tendency of an atom to lose electrons. Potassium would readily lose electrons instead of gaining.

Between Arsenic and Selenium: Arsenic belongs to group V and Selenium group VI. The two elements both belong to period IV on the periodic table. Across a period, electron affinity increases due to increase in nuclear charge. Therefore, Selenium would have a greater electron affinity compared to Arsenic.

Fluorine has the highest electron affinity of all. It needs just an electron to complete its octet.