Answer:

The [Sc(H2O)6]3+ ion is a complex ion where a central scandium ion (Sc3+) is surrounded by six water molecules (H2O). Let's analyze each option to determine the correct answer.

a) Colorless and diamagnetic:
Colorless: This option suggests that the complex ion does not have any color.
Diamagnetic: This option suggests that the complex ion does not have any unpaired electrons and is not attracted to a magnetic field.

b) Colored and octahedral:
Colored: This option suggests that the complex ion has a color.
Octahedral: This option suggests that the complex ion has an octahedral geometry, where the central ion is surrounded by six ligands arranged in an octahedral shape.

c) Colorless and paramagnetic:
Colorless: This option suggests that the complex ion does not have any color.
Paramagnetic: This option suggests that the complex ion has unpaired electrons and is attracted to a magnetic field.

d) Colored and paramagnetic:
Colored: This option suggests that the complex ion has a color.
Paramagnetic: This option suggests that the complex ion has unpaired electrons and is attracted to a magnetic field.

Based on the given options, the correct answer is option 'a' - colorless and diamagnetic.

Explanation:
The [Sc(H2O)6]3+ ion is a complex ion of scandium (Sc3+) surrounded by six water molecules (H2O). Scandium is a transition metal, and its ions often form complexes with ligands. In this case, the ligands are water molecules.

The complex ion [Sc(H2O)6]3+ has a d0 electronic configuration, meaning that the central scandium ion has no unpaired electrons. Consequently, the complex ion is diamagnetic because there are no unpaired electrons to be attracted to a magnetic field.

Additionally, the complex ion does not exhibit any color because the energy difference between the d orbitals of the central ion is relatively small, resulting in no visible absorption of light.

Hence, the correct answer is option 'a' - colorless and diamagnetic.