Answer the question on the basis of passage given below:

All transition elements display typical metallic properties like high melting point, boiling point, tensile strength, high malleability and ductility, luster, etc. Their metallic character increases down the group and elements of 4d and 5d series exhibit higher metallic characters. They show variable oxidation states and forms a number of coloured compounds due to the presence of unpaired electrons which shows d-d transitions and makes them paramagnetic.

Which of the following will be coloured in aqueous medium?

$Cu^{2+}$

The correct answer is Option (2) → $Cu^{2+}$.

To determine which of the given metal ions will be colored in an aqueous medium, we need to consider their electronic configurations and how they interact with light.

1. Sc\(^{3+}\) (Scandium)

Configuration: Sc has an atomic number of 21. The electron configuration is \([Ar] 3d^{1} 4s^{2}\).

Sc\(^{3+}\) loses 3 electrons, resulting in the configuration \([Ar]\), which means it has no d-electrons.

Color: Colorless in solution, as there are no unpaired d-electrons to absorb visible light

2. Cu\(^{2+}\) (Copper)

Configuration: Cu has an atomic number of 29. The electron configuration is \([Ar] 3d^{10} 4s^{1}\).

Cu\(^{2+}\) loses two electrons, resulting in the configuration \([Ar] 3d^{9}\).

Color: Colored (blue in aqueous solution) due to the presence of unpaired d-electrons, which can transition between energy levels upon absorbing certain wavelengths of light.

3. Zn\(^{2+}\) (Zinc)

Configuration: Zn has an atomic number of 30. The electron configuration is \([Ar] 3d^{10} 4s^{2}\).

Zn\(^{2+}\) loses two electrons, resulting in the configuration \([Ar] 3d^{10}\).

Color: Colorless in solution, as all d-orbitals are fully filled (no unpaired electrons).

4. Cd\(^{2+}\) (Cadmium)

Configuration: Cd has an atomic number of 48. The electron configuration is \([Kr] 4d^{10} 5s^{2}\).

Cd\(^{2+}\) loses two electrons, resulting in the configuration \([Kr] 4d^{10}\).

Color: Colorless in solution, as all d-orbitals are fully filled.

Conclusion

Among the given options, only Cu\(^{2+}\) will be colored in an aqueous medium. The others (Sc\(^{3+}\), Zn\(^{2+}\), and Cd\(^{2+}\)) are colorless due to the absence of unpaired d-electrons.

Therefore, the correct answer is: Cu\(^{2+}\).