Question

Arrange the following ions in increasing order of number of 3d-electrons: (A) Cr$^{2+}$
(B) Cu$^{2+}$
(C) Ti$^{3+}$
(D) Mn$^{2+}$

• A. (B), (A), (C), (D)
• B. (C), (A), (D), (B)
• C. (C), (D), (A), (B)
• D. (D), (B), (C), (A)

Hint:

When determining the number of d-electrons in transition metal ions, remember that electrons are removed first from the 4s orbital before the 3d orbital.

Answer 1

The Correct Option is C

Determine the number of 3d-electrons in each ion. Step 1: Electron configuration of neutral atoms. - Chromium (Cr), Z=24: \[ \text{Cr}: [Ar] \, 3d^5 \, 4s^1 \] - Copper (Cu), Z=29: \[ \text{Cu}: [Ar] \, 3d^{10} \, 4s^1 \] - Titanium (Ti), Z=22: \[ \text{Ti}: [Ar] \, 3d^2 \, 4s^2 \] - Manganese (Mn), Z=25: \[ \text{Mn}: [Ar] \, 3d^5 \, 4s^2 \] Step 2: Electron configuration of the ions. - For Cr$^{2+}$: Remove 2 electrons from 4s, then 3d. Configuration: \[ \text{Cr}^{2+}: [Ar] \, 3d^4 \] Number of 3d-electrons = 4. - For Cu$^{2+}$: Remove 2 electrons from 4s, then 3d. Configuration: \[ \text{Cu}^{2+}: [Ar] \, 3d^9 \] Number of 3d-electrons = 9. - For Ti$^{3+}$: Remove 3 electrons from 4s, then 3d. Configuration: \[ \text{Ti}^{3+}: [Ar] \, 3d^1 \] Number of 3d-electrons = 1. - For Mn$^{2+}$: Remove 2 electrons from 4s, then 3d. Configuration: \[ \text{Mn}^{2+}: [Ar] \, 3d^5 \] Number of 3d-electrons = 5. Step 3: Arrange ions in increasing order of 3d-electrons. - Ti$^{3+}$: 1 3d-electron. - Cr$^{2+}$: 4 3d-electrons. - Mn$^{2+}$: 5 3d-electrons. - Cu$^{2+}$: 9 3d-electrons. The increasing order is: Ti$^{3+}$ (1)<Cr$^{2+}$ (4)<Mn$^{2+}$ (5)<Cu$^{2+}$ (9). Final Answer: \[ \boxed{\text{The correct order is Ti^{3+}, Cr^{2+}, Mn^{2+}, Cu^{2+}.}} \]