Which element would most likely have an electron affinity measuring closest to zero? na al rb ar

The answer is:

Ar

The explanation:

when:

-electron affinity goes through the periodic table from left to right and from down to up  as shown in the attached pic.

and:

when The Electron affinity is  the change in energy  of a neutral atom (in its gaseous phase) when a negative ion forms when an electron is added . In other words, the neutral atom's like of gaining an electron.

-electron affinity is the ability of an atom to accept an electron.

-Unlike electronegativity, electron affinity is a quantitative measurement of the energy change that happens when an electron is added to a neutral gas atom.

-The more negative the electron affinity value, the higher an atom's affinity for electrons.

so, according to that and according to the attached pic so, the answer is Ar

The activity series is shown in the attached picture. if the element is below the other, then you can displace the other. following the activity series as a guide, the reactions are as follows: nickel and aluminum chloride3 ni + 2 alcl₃  → 3 nicl₂ + 2 albarium and copper bromideba + cubr  →  no reaction because cu is less oxidizable than bapotassium nitrate and aluminum3 kno₃ + al  → al(no₃)₃ + 3 ksodium phosphate and zincnaso₄ + zn  → znso₄ + na

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts