Question

The pair in which both species have same magnetic moment (spin only value) is:

• A. \( \left[ \text{Cr(H}_2 \text{O})_6 \right]^{2+} \), \( \left[ \text{CoCl}_4 \right]^{2-} \)
• B. \( \left[ \text{Cr(H}_2 \text{O})_6 \right]^{3+} \), \( \left[ \text{Fe(H}_2 \text{O})_6 \right]^{2+} \)
• C. \( \left[ \text{Mn(H}_2 \text{O})_6 \right]^{2+} \), \( \left[ \text{Fe(H}_2 \text{O})_6 \right]^{2+} \)
• D. \( \left[ \text{CoCl}_4 \right]^{2-} \), \( \left[ \text{Fe(H}_2 \text{O})_6 \right]^{2+} \)

Hint:

The magnetic moment depends on the number of unpaired electrons. Species with the same number of unpaired electrons will have the same magnetic moment.

Answer 1

The Correct Option is B

Step 1: Magnetic moment and spin-only formula.
The magnetic moment is given by the formula \( \mu_{\text{eff}} = \sqrt{n(n+2)} \), where \( n \) is the number of unpaired electrons.
Step 2: Determine the species with the same magnetic moment.
Both \( \left[ \text{Cr(H}_2 \text{O})_6 \right]^{3+} \) and \( \left[ \text{Fe(H}_2 \text{O})_6 \right]^{2+} \) have the same number of unpaired electrons and thus the same magnetic moment. Final Answer: \[ \boxed{\left[ \text{Cr(H}_2 \text{O})_6 \right]^{3+}, \left[ \text{Fe(H}_2 \text{O})_6 \right]^{2+}} \]