The aqueous solution containing which one of the following ions will be colourless

\(Sc^{3+}\)

The correct answer is option 1.\(Sc^{3+}\).

Out of the given ions, the aqueous solution containing \(Sc^{3+}\) (Scandium ion) will be colourless.

The color of a transition metal ion in solution depends on the presence of unpaired electrons in its \(d\)-orbitals. These unpaired electrons can absorb visible light, leading to the colored solution.

\(Sc^{3+}\) (Scandium): This ion has a noble gas electron configuration \((3s^23p^6)\) after losing its three valence electrons. Since there are no d-electrons (all filled), \(Sc^{3+}\) has no unpaired electrons and hence, its solution is colourless.

\(Fe^{2+}\) (Iron): Iron(II) has the electron configuration \(3d^6\). It possesses six unpaired electrons in its d-orbitals, resulting in a colored solution (usually pale green or light blue).

\(Ti^{3+}\) (Titanium): This ion has the configuration 3d¹. With one unpaired electron, \(Ti^{3+}\) solutions exhibit color (often lavender or purple).

\(Mn^{2+}\) (Manganese): Manganese(II) has the configuration \(3d^5\). Here, five d-orbitals hold unpaired electrons, leading to a colored solution (usually a pale pink).

Therefore, \(Sc^{3+}\), lacking any d-electrons, forms a colourless solution.