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

Concept (Colour of transition-metal ions): An ion is coloured if it has partially filled \(d\)-orbitals (i.e., \(d^1\)–\(d^9\)). Ions with \(d^0\) or \(d^{10}\) configurations are generally colourless.
Step 1: Check each pair in Statement I
\(\text{Sc}^{3+}\) : \(d^0\) (colourless), \(\text{Ti}^{3+}\) : \(d^1\) (coloured) \(\Rightarrow\) Not both coloured.
\(\text{Mn}^{2+}\) : \(d^5\) (coloured, pale pink), \(\text{Cr}^{2+}\) : \(d^4\) (coloured) \(\Rightarrow\) Both coloured \(\checkmark\).
\(\text{Cu}^{2+}\) : \(d^9\) (coloured), \(\text{Zn}^{2+}\) : \(d^{10}\) (colourless) \(\Rightarrow\) Not both coloured.
\(\text{Ni}^{2+}\) : \(d^8\) (coloured), \(\text{Ti}^{4+}\) : \(d^0\) (colourless) \(\Rightarrow\) Not both coloured. Only \([\text{Mn}^{2+},\text{Cr}^{2+}]\) satisfies the condition. Hence, Statement I is false. Concept (Reducing agents): A strong reducing agent is easily oxidised (loses electrons).
Step 2: Analyse Statement II
\(\text{Ti}^{4+}\) is already in a high oxidation state and tends to act as an {oxidising agent}, not a reducing agent.
\(\text{Eu}^{2+}\) readily oxidises to \(\text{Eu}^{3+}\) and is known to be a strong reducing agent. Thus, Statement II is also false. Final Conclusion: \[ \boxed{\text{Both Statement I and Statement II are false}} \]