Question

Ti(H2O)6 is coloured while [SC(H2O)6]3+ is colorless?

Answer 1

This is because, Ti(H2o)6 has unpaired electron for d-d transition so it is coloured .while Sc(H2o)6 can not undergo d-d Transition so it is colourles.

Answer 2

Answer: $Ti(H_2O)_6$ is colored due to presence of unpaired electrons while $[Sc(H_2O)_6]^{3+}$ is colorless due to the absence of unpaired electrons.

Explanation:  

1) $Ti(H_2O)_6$ has titanium in zero oxidation state as water is a neutral ligand.

Atomic number of titanium is 22 and contains 22 electrons.

The electronic configuration of titanium will be,

$Ti:22:1s^22s^23s^23p^64s^23d^2$

As it contains unpaired electrons in d orbitals, they can transition between orbitals and thus produce color.

2) $[Sc(H_2O)_6]^{3+}$ has scandium in +3 oxidation state as water is a neutral ligand.

Atomic number of scandium is 21 and contains 21 electrons.

The electronic configuration of titanium will be,

$Sc:21:1s^22s^23s^23p^64s^23d^1$

$Sc^{3+}:18:1s^22s^23s^23p^6$

As it contains no unpaired electrons, they do not show any color.