The intensity of color in a solution is generally associated with the presence of transition metal ions and the extent of $d-d$ transitions or charge transfer transitions they undergo. In the case of manganese compounds, the Mn ion can exhibit different oxidation states, each with distinct colors:

$1.\,\,\,\,\,\left[\mathrm{Mn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right] \mathrm{Cl}_2$ : This complex contains $\mathrm{Mn}^{2+}$ ions. $\mathrm{Mn}^{2+}$ typically has a pale pink color due to weak d -d transitions.

$2.\,\,\,\,\,\left[\mathrm{Mn}\left(\mathrm{NH}_3\right)_6\right] \mathrm{Cl}_3$ : This complex contains $\mathrm{Mn}^{3+}$ ions. $\mathrm{Mn}^{3+}$ is not stable in aqueous solution and typically oxidizes water to produce $\mathrm{MnO}_2$, which is a brown precipitate. The solution would not be intensely colored.

$3.\,\,\,\,\,\left[\mathrm{Mn}\left(\mathrm{NH}_3\right)_5 \mathrm{Cl}\right] \mathrm{Cl}$ : This complex likely contains $\mathrm{Mn}^{2+}$ ions, similar to the first complex, but with different ligands, leading to slightly different colors.

$4.\,\,\,\,\,\mathrm{KMnO}_4$ : Potassium permanganate $\left(\mathrm{KMnO}_4\right)$ contains Mn in the +7 oxidation state, and it is well known for its intense purple color due to strong charge transfer transitions.

Among these, $\mathrm{KMnO}_4$ (potassium permanganate) gives the most intense color due to the presence of Mn in the +7 oxidation state, which leads to strong charge transfer transitions that result in a deep purple color. Therefore, the answer is:

$$ \text { D. } 0.1 \mathrm{M} \mathrm{KMnO}_4 $$

Physical Chemistry

Inorganic Chemistry

Organic Chemistry

Coordination Compounds · Chemistry · IAT (IISER)

MCQ (Single Correct Answer)