Question

Identify the correct decreasing order of stability of complexes formed by divalent metal ions with same ligand.

• A. \(\mathrm{Co}^{2+}>\mathrm{Fe}^{2+}>\mathrm{Ni}^{2+}\)
• B. \(\mathrm{Fe}^{2+}>\mathrm{Co}^{2+}>\mathrm{Ni}^{2+}\)
• C. \(\mathrm{Ni}^{2+}>\mathrm{Co}^{2+}>\mathrm{Fe}^{2+}\)
• D. \(\mathrm{Ni}^{2+}>\mathrm{Fe}^{2+}>\mathrm{Co}^{2+}\)

Hint:

The stability of complexes of divalent first-row metal ions with the same ligand follows the Irving-Williams series.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
For divalent ions of the first transition series, complex stability with a given ligand follows the Irving-Williams order, which increases as the ionic radius decreases and crystal field stabilisation rises.

Step 2: Apply the series
The order of increasing stability is \(\text{Mn}^{2+} \lt \text{Fe}^{2+} \lt \text{Co}^{2+} \lt \text{Ni}^{2+} \lt \text{Cu}^{2+}\).

Step 3: Compare the options
For the decreasing order among the three given ions, \(\text{Ni}^{2+} > \text{Co}^{2+} > \text{Fe}^{2+}\).

Final Answer:
The decreasing order of stability is Ni, then Co, then Fe. \[ \boxed{\text{(C) }\text{Ni}^{2+}>\text{Co}^{2+}>\text{Fe}^{2+}} \]