Arrange the following atoms and/or ions in the order of increasing size: Br ^–, Kr, Rb⁺, Sr²⁺.

• A. Kr < Br^- < Sr²⁺ < Rb⁺
• B. Kr < Sr²⁺ < Rb⁺ < Br^-
• C. Sr²⁺ < Rb⁺ < Kr < Br^-
• D. Rb⁺ < Sr²⁺ < Kr < Br^-
• E. Br^- < Kr < Rb⁺ < Sr²⁺

Answer: (C)

Verified step by step guidance

1. Identify the number of protons and electrons for each species: Br⁻, Kr, Rb⁺, and Sr²⁺. This will help determine their effective nuclear charge and electron configuration.
2. Understand that ions with the same number of electrons (isoelectronic species) will have different sizes based on their nuclear charge. The more protons, the smaller the ion, because the electrons are pulled closer to the nucleus.
3. Compare the electron configurations: Br⁻ has gained an electron, Kr is a noble gas with a full outer shell, Rb⁺ has lost an electron, and Sr²⁺ has lost two electrons. This affects their size.
4. Consider the effective nuclear charge: Br⁻ has the least nuclear charge for its electron count, making it larger. Sr²⁺ has the most nuclear charge for its electron count, making it smaller.
5. Arrange the species in order of increasing size based on the above analysis: Sr²⁺ < Rb⁺ < Kr < Br⁻.