Final answer:
The element with the most similar electron arrangement to potassium is sodium, as both are alkali metals in Group 1 with a single s electron in their valence shells, corresponding to [Ar]4s¹ for potassium and [Ne]3s¹ for sodium respectively. So the correct answer is Option A.
Step-by-step explanation:
The element that will have an electron arrangement most similar to potassium (K) is sodium (Na). Potassium is an alkali metal with an atomic number of 19 and has a single s electron in its valence shell, which is the 4s orbital ([Ar]4s¹). Elements in the same group of the periodic table have the same number of valence electrons, which contributes to similar chemical properties. Since both sodium and potassium are in Group 1, they share this electron configuration characteristic, making sodium similar to potassium in terms of valence electron arrangement. Sodium, with atomic number 11, has its valence electron in the 3s orbital ([Ne]3s¹).
Chlorine (Cl), argon (Ar), and phosphorus (P) do not have a similar electron arrangement as they belong to different groups with a different number of valence electrons. Therefore, the correct answer to which element will have an electron arrangement most similar to potassium is A. sodium.