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

Answer: (A)

2

Answer 2

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).