Question

Why is Sc+3 colourless,while Ti+3 coloured

Answer 1

This is due to the reason that Scandium 3+ has no unpaired electrons whereas Ti 3+ has unpaired electron in his sub Shetland thus it is coloured compound.

Answer 2

because scandium3+ has no umpaired of electrons and titanium +3 has unpaired of electrons so they combine and make a colour