Which of the following ions would be colored in aqueous solution?

• A. Cu^{2+}
• B. Na^{+}
• C. Cl^{-}
• D. K^{+}

Answer: (A)

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.
2. Identify the ions given: \(\mathrm{Cu^{2+}}\), \(\mathrm{Na^{+}}\), \(\mathrm{Cl^{-}}\), and \(\mathrm{K^{+}}\).
3. 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.
4. 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.
5. Conclude that among the given ions, only \(\mathrm{Cu^{2+}}\) will be colored in aqueous solution due to its electronic structure.