Final answer:
Charge density is determined by the size of the ion and its charge, with smaller ions having higher charge densities. Positive ions with higher charges and smaller sizes, such as the copper(I) ion, tend to have higher charge densities than larger ions like I⁻, but the hydrogen ion has the highest charge density.
Step-by-step explanation:
When considering which anion or cation exhibits the highest charge density, it is important to assess the size of the ion relative to its charge. Charge density is the charge of an ion divided by its volume. Smaller ions with higher charges will have higher charge densities.
The provided options for the anions and cations include copper(I) ion or cuprous ion, chloride anions, the calcium ion, the sulfide ion, the sulfite ion, the ammonium ion, and others such as As³⁻, Br⁻, K+, and Mg2+. Among these, positive ions like Mg2+, which have small sizes and a +2 charge, tend to have larger charge densities than larger, singly-charged negative ions like I⁻. Furthermore, the copper(I) ion also has a +1 charge but is smaller than the iodide ion, which potentially gives it a higher charge density. However, the hydrogen ion (H⁻), due to its extremely small size, has the highest charge density of any ion.