Question

The pairs of ions which exhibit same colour in aquated state are: I. \[ Fe^{2+}, Ni^{2+} \] II. \[ V^{2+}, Cr^{2+} \] III. \[ Cr^{2+}, Cu^{2+} \]

• A. I, II only
• B. II, III only
• C. I, II, III
• D. I, III only

Hint:

Important colours: \[ Cu^{2+} \rightarrow \text{Blue} \] \[ Cr^{2+} \rightarrow \text{Blue} \] \[ Ni^{2+} \rightarrow \text{Green} \] \[ Fe^{2+} \rightarrow \text{Pale Green} \]

Answer 1

The Correct Option is D

Concept: Transition metal ions show characteristic colours due to \(d-d\) transitions.

Step 1: Recall colours of hydrated ions.
\[ Fe^{2+} \rightarrow \text{Pale Green} \] \[ Ni^{2+} \rightarrow \text{Green} \] Hence pair I is considered similar. \[ V^{2+} \rightarrow \text{Violet} \] \[ Cr^{2+} \rightarrow \text{Blue} \] Pair II does not show the same colour. \[ Cr^{2+} \rightarrow \text{Blue} \] \[ Cu^{2+} \rightarrow \text{Blue} \] Pair III exhibits the same colour.

Step 2: Select the correct pairs.
Correct pairs are I and III. \[ \boxed{\text{I and III only}} \]