Question

Which of the following elements is colourless?

• A. Ti\(^{4+}\)
• B. Fe\(^{2+}\)
• C. Fe\(^{3+}\)
• D. None of these

Hint:

Metal ions with completely filled or empty d-orbitals (like Ti\(^{4+}\)) do not absorb visible light, making them colourless.

Answer 1

The Correct Option is A

The colour of a metal ion in solution is due to the presence of partially filled d-orbitals that can absorb light in the visible region.
- Ti\(^{4+}\) has no d-electrons and therefore does not absorb light in the visible region, making it colourless.
- Fe\(^{2+}\) and Fe\(^{3+}\) both have partially filled d-orbitals, which absorb light in the visible region and give the solutions a colour. Thus, the correct answer is option (A).