Question

The correct set of ions (aqueous solution) with the same colour from the following is:

• A. \( V^{2+} \), \( Cr^{3+} \), \( Mn^{3+} \)
• B. \( Zn^{2+} \), \( V^{3+} \), \( Fe^{3+} \)
• C. \( Ti^{4+} \), \( V^{4+} \), \( Mn^{2+} \)
• D. \( Sc^{3+} \), \( Ti^{3+} \), \( Cr^{2+} \)

Hint:

The colour of transition metal ions in aqueous solutions is determined by the d-electron configuration and the ligand field around the ion. Ions that are part of the same group or period often exhibit similar colours due to similar electronic transitions.

Answer 1

The Correct Option is A

Transition metals and their ions often exhibit characteristic colors due to d-d transitions where electrons in the d-orbitals absorb specific wavelengths of light and move to higher energy levels. The color observed is complementary to the color of light absorbed. Here is the breakdown of each ion:

Set 1: \( V^{2+} \), \( Cr^{3+} \), \( Mn^{3+} \)

These ions are known to produce similar colors in solution. Specifically, they appear in shades of violet or blue-green. The colors arise from specific d-d transitions unique to each ion, but similar enough to result in perceived color similarity:

• \( V^{2+} \): Blue or violet
• \( Cr^{3+} \): Often green
• \( Mn^{3+} \): Typically red-violet

Set 2: \( Zn^{2+} \), \( V^{3+} \), \( Fe^{3+} \)

\( Zn^{2+} \) has a completely filled d-orbital, resulting in a colorless solution, thus not matching the others which may appear yellow to brown.

Set 3: \( Ti^{4+} \), \( V^{4+} \), \( Mn^{2+} \)

\( Ti^{4+} \) usually produces a colorless solution due to its electronic configuration, whereas the other ions have visible colors.

Set 4: \( Sc^{3+} \), \( Ti^{3+} \), \( Cr^{2+} \)

\( Sc^{3+} \) is colorless in solution due to its lack of d-electrons, and thus, this set does not have similar colors either.

Thus, the correct set of ions that produce similarly colored aqueous solutions is \( V^{2+} \), \( Cr^{3+} \), \( Mn^{3+} \), due to their ability to exhibit complementary colored transitions in solutions.