Question

Which of the following is colorless in aqueous solution?
(A) $ F{e^{3 + }} $
(B) $ M{n^{2 + }} $
(C) $ T{i^{3 + }} $
(D) $ S{c^{3 + }} $

Answer 1

Hint :This question is based on the concept of presentation of colors by the transition elements. This is caused due to the presence of unpaired electrons in the atomic configuration of an element. The unpaired electrons are responsible for the release of color thus showing a colored aqueous solution with the ions of that element.

Complete Step By Step Answer:
Most chemical substances, such as sodium chloride (table salt), aluminium oxide, naphthalene (moth flakes), and diamond, are colourless when pure. All of the electrons in these compounds are paired. These paired electrons are extremely stable, and being unpaired and forming excited energy levels requires extremely high energies.
Only UV light has enough energy to be absorbed, explaining why there are no visible light absorptions and no colour. Coloured salts are produced by the compounds of a number of metals, the most frequent of which being iron, chromium, nickel, cobalt, and manganese. These metals are transition elements, meaning their compounds include unpaired electrons. These unpaired electrons easily generate excited energy states, resulting in photon absorption and the generation of colour.
In the above question, $ F{e^{3 + }} $ , $ M{n^{2 + }} $ and $ T{i^{3 + }} $ are colored since they have unpaired electrons. So, electrons are excited and they produce colored solutions of these ions. $ S{c^{3 + }} $ , on the other hand, has no unpaired electrons in its electronic configuration. So, it cannot produce coloured solution.

Note :
In general, color is generated by a substance (such as a gemstone) absorbing some wavelengths of light while allowing other wavelengths to flow through unaffected. The ultimate hue of the gemstone is determined by the wavelengths that travel through it.