A student adds an excess of concentrated hydrochloric acid to a test tube containing a pale blue aqueous solution of copper(II) sulfate. The solution changes color to form a yellow-green solution.
Which complex ion is responsible for this yellow-green color?
[CuCl6]4−[\text{Cu}\text{Cl}_6]^{4-}[CuCl6]4−
[Cu(H2O)4Cl2][\text{Cu}(\text{H}_2\text{O})_4\text{Cl}_2][Cu(H2O)4Cl2]
[CuCl4]2−[\text{Cu}\text{Cl}_4]^{2-}[CuCl4]2−
[CuCl4]2+[\text{Cu}\text{Cl}_4]^{2+}[CuCl4]2+
