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Multiple Choice
Which of the following ions would be colored in aqueous solution?
A
Cu^{2+}
B
Na^{+}
C
Cl^{-}
D
K^{+}
Verified step by step guidance
1
Understand that the color of ions in aqueous solution is generally due to the presence of unpaired d-electrons in transition metal ions, which allow d-d electronic transitions that absorb visible light.
Identify the ions given: $\mathrm{Cu^{2+}}$, $\mathrm{Na^{+}}$, $\mathrm{Cl^{-}}$, and $\mathrm{K^{+}}$.
Recognize that $\mathrm{Na^{+}}$, $\mathrm{Cl^{-}}$, and $\mathrm{K^{+}}$ are not transition metal ions and have either completely filled electron shells or no d-electrons, so they do not exhibit color in aqueous solution.
Note that $\mathrm{Cu^{2+}}$ is a transition metal ion with an incomplete d-subshell, which allows electronic transitions that absorb certain wavelengths of visible light, resulting in a colored solution.
Conclude that among the given ions, only $\mathrm{Cu^{2+}}$ will be colored in aqueous solution due to its electronic structure.