Question

Which of the following is a colourless transition metal ion?

• A. \(Ca^{2+}\)
• B. \(Cr^{3+}\)
• C. \(Ti^{4+}\)
• D. \(Fe^{2+}\)
• E. \(Fe^{3+}\)

Hint:

Transition metal ions with \(d^0\) or \(d^{10}\) configuration are colourless.

Answer 1

The Correct Option is C

Concept: Colour in transition metal ions arises due to \(d\text{-}d\) electronic transitions. If no \(d\)-electrons are present, the ion is colourless.

Step 1: Check electronic configuration.

• \(Ca^{2+}\) $\rightarrow$ Not a transition metal
• \(Cr^{3+}\) $\rightarrow$ \(d^3\) → coloured
• \(Ti^{4+}\) $\rightarrow$ \(d^0\) → colourless
• \(Fe^{2+}\) $\rightarrow$ \(d^6\) → coloured
• \(Fe^{3+}\) $\rightarrow$ \(d^5\) → coloured

Step 2: Select correct ion.
Only \(Ti^{4+}\) has no \(d\)-electrons.