The hydrated cations of first transition series that imparts a blue color:
Correct answer: A. Cr2+, Co2+, Cu2+
- A. Cr2+, Co2+, Cu2+
- B. Cu2+, Zn2+, Ti4+
- C. Ti3+, Zn2+, Cu2+
- D. Cr3+, Ti4+, Cu2+
Explanation
The correct answer is Option A: Cr2+, Co2+, Cu2+. These transition metal ions possess unpaired d-electrons, allowing for d-d electronic transitions. When light passes through a solution containing these ions, specific wavelengths are absorbed, and others are emitted, giving rise to their characteristic blue color. Option B is incorrect because Zn2+ has a fully filled d-orbital, preventing d-d transitions. Option C is incorrect because Zn2+ does not exhibit color due to its filled d-orbital, even though Ti3+ and Cu2+ can be colored. Option D is incorrect because Ti4+ lacks d-electrons, thus cannot contribute to color, despite Cr3+ and Cu2+ being potentially colored.
This question appeared on the ETEA MDCAT 2016 paper, which you can sit online with every answer explained.
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About Electronic Structure of d-Block Elements
The electronic structure of d-block elements covers the filling of the (n-1)d and ns orbitals, general electronic configurations, and the exceptions shown by chromium and copper. It explains how partially filled d orbitals produce variable oxidation states, coloured ions, magnetic behaviour and complex formation, while distinguishing transition elements from elements with completely filled d subshells.
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