Question

Given below are two statements: Statement I: The number of pairs, from the following, in which {both the ions are coloured} are \([\text{Sc}^{3+},\text{Ti}^{3+}]\), \([\text{Mn}^{2+},\text{Cr}^{2+}]\), \([\text{Cu}^{2+},\text{Zn}^{2+}]\) and \([\text{Ni}^{2+},\text{Ti}^{4+}]\). Statement II: \(\text{Ti}^{4+}\) is the strongest reducing agent among \(\text{Th}^{4+}, \text{Ce}^{4+}, \text{Gd}^{3+}\) and \(\text{Eu}^{2+}\). In the light of the above statements, choose the correct answer.

• A. Statement I is true but Statement II is false
• B. Statement I is false but Statement II is true
• C. Both Statement I and Statement II are false
• D. Both Statement I and Statement II are true

Hint:

Colour in transition-metal ions depends on partially filled \(d\)-orbitals, while reducing power increases with ease of oxidation.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Colour in transition metal ions is typically due to \(d-d\) transitions, which require partially filled \(d\)-orbitals (\(d^1\) to \(d^9\)). Ions with \(d^0\) or \(d^{10}\) configurations are generally colourless.
Step 2: Detailed Explanation:
Evaluation of Statement I:
1. \([Sc^{3+}, Ti^{3+}]\) : \(Sc^{3+}\) is \(d^0\) (colourless), \(Ti^{3+}\) is \(d^1\) (coloured). Pair is NOT both coloured.
2. \([Mn^{2+}, Cr^{3+}]\) : \(Mn^{2+}\) is \(d^5\) (coloured), \(Cr^{3+}\) is \(d^3\) (coloured). Pair IS both coloured.
3. \([Cu^{2+}, Zn^{2+}]\) : \(Cu^{2+}\) is \(d^9\) (coloured), \(Zn^{2+}\) is \(d^{10}\) (colourless). Pair is NOT both coloured.
4. \([Ni^{2+}, Ti^{4+}]\) : \(Ni^{2+}\) is \(d^8\) (coloured), \(Ti^{4+}\) is \(d^0\) (colourless). Pair is NOT both coloured.
Only 1 pair consists of both coloured ions. Statement I claims there are 3 such pairs, so it is False.
Evaluation of Statement II:
\(Th^{4+}\) has an \(f^0\) configuration and is the most stable oxidation state for Thorium; it is not a reducing agent. In the given list, \(Eu^{2+}\) (\([Xe] 4f^7\)) is a well-known strong reducing agent as it tends to get oxidized to the more stable \(Eu^{3+}\) state. Statement II is False.
Step 3: Final Answer:
Both Statement I and Statement II are false.