Which of the following ions is isoelectronic with Ar?

• A. Ca2+
• B. Na+
• C. K+
• D. Cl-

Answer: (D)

Verified step by step guidance

1. Recall that two species are isoelectronic if they have the same number of electrons.
2. Determine the number of electrons in the neutral Argon (Ar) atom. Argon has an atomic number of 18, so it has 18 electrons.
3. Calculate the number of electrons for each ion by adjusting the number of electrons in the neutral atom by the charge of the ion: - For Ca^{2+}, subtract 2 electrons from calcium's atomic number (20). - For Na^{+}, subtract 1 electron from sodium's atomic number (11). - For K^{+}, subtract 1 electron from potassium's atomic number (19). - For Cl^{-}, add 1 electron to chlorine's atomic number (17).
4. Compare the number of electrons in each ion to the 18 electrons of Argon to identify which ions are isoelectronic with Ar.
5. Select the ions that have exactly 18 electrons, as these are isoelectronic with Argon.