Final answer:
The statement that Cl⁻ ion and K⁺ ion are isoelectronic is true because both end up having the same electron configuration [Ne]3s²3p⁶, which is equivalent to the electron configuration of Argon.
Step-by-step explanation:
Whether the Cl⁻ ion and the K⁺ ion are isoelectronic is a true statement. Being isoelectronic means they have the same number of electrons.
Chlorine has an electron configuration of [Ne]3s²3p⁵ as an atom, and it gains one electron to become Cl⁻, resulting in the noble gas configuration of [Ne]3s²3p⁶.
Potassium has an electron configuration of [Ar]4s¹ as an atom, and it loses one electron to become K⁺, also resulting in the configuration [Ne]3s²3p⁶. This makes Cl⁻ and K⁺ isoelectronic because they have identical electron configurations, mirroring that of the noble gas argon.