Question

Number of complexes from the following with even number of unpaired "d" electrons is _____. \[ [\text{V}(\text{H}_2\text{O})_6]^{3+}, \, [\text{Cr}(\text{H}_2\text{O})_6]^{2+}, \, [\text{Fe}(\text{H}_2\text{O})_6]^{3+}, \, [\text{Ni}(\text{H}_2\text{O})_6]^{3+}, \, [\text{Cu}(\text{H}_2\text{O})_6]^{2+}\] [Given atomic numbers: \( \text{V} = 23, \, \text{Cr} = 24, \, \text{Fe} = 26, \, \text{Ni} = 28, \, \text{Cu} = 29 \)]

• A. 2
• B. 4
• C. 5
• D. 1

Answer 1

The Correct Option is A

Determine the Electronic Configuration of Each Metal Ion:

For \([V(\text{H}_2\text{O})_6]^{3+}:\)

Vanadium (V) has an atomic number of 23, with an electronic configuration of \([ \text{Ar} ] 3d^3 4s^2\). \(\text{V}^{3+}\) configuration: \([ \text{Ar} ] 3d^2\). Number of unpaired \(d\)-electrons: 2 (even number).

For \([Cr(\text{H}_2\text{O})_6]^{2+}:\)

Chromium (Cr) has an atomic number of 24, with an electronic configuration of \([ \text{Ar} ] 3d^5 4s^1\). \(\text{Cr}^{2+}\) configuration: \([ \text{Ar} ] 3d^4\). Number of unpaired \(d\)-electrons: 4 (even number).

For \([Fe(\text{H}_2\text{O})_6]^{3+}:\)

Iron (Fe) has an atomic number of 26, with an electronic configuration of \([ \text{Ar} ] 3d^6 4s^2\). \(\text{Fe}^{3+}\) configuration: \([ \text{Ar} ] 3d^5\). Number of unpaired \(d\)-electrons: 5 (odd number).

For \([Ni(\text{H}_2\text{O})_6]^{3+}:\)

Nickel (Ni) has an atomic number of 28, with an electronic configuration of \([ \text{Ar} ] 3d^8 4s^2\). \(\text{Ni}^{3+}\) configuration: \([ \text{Ar} ] 3d^7\). Number of unpaired \(d\)-electrons: 3 (odd number).

For \([Cu(\text{H}_2\text{O})_6]^{2+}:\)

Copper (Cu) has an atomic number of 29, with an electronic configuration of \([ \text{Ar} ] 3d^{10} 4s^1\). \(\text{Cu}^{2+}\) configuration: \([ \text{Ar} ] 3d^9\). Number of unpaired \(d\)-electrons: 1 (odd number).

Count Complexes with Even Number of Unpaired Electrons:

From the analysis above, only \([V(\text{H}_2\text{O})_6]^{3+}\) and \([Cr(\text{H}_2\text{O})_6]^{2+}\) have an even number of unpaired \(d\)-electrons.

Conclusion:

The number of complexes with an even number of unpaired \(d\)-electrons is 2, corresponding to Option (1).