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

We need to find the number of 3d-electrons in each of the ions.
Step 1: Electron configuration of neutral atoms.
- Chromium (Cr) has an atomic number of 24, so its electron configuration is: \[ \text{Cr}: [Ar] \, 3d^5 \, 4s^1 \] - Copper (Cu) has an atomic number of 29, so its electron configuration is: \[ \text{Cu}: [Ar] \, 3d^{10} \, 4s^1 \] - Titanium (Ti) has an atomic number of 22, so its electron configuration is: \[ \text{Ti}: [Ar] \, 3d^2 \, 4s^2 \] - Manganese (Mn) has an atomic number of 25, so its electron configuration is: \[ \text{Mn}: [Ar] \, 3d^5 \, 4s^2 \] Step 2: Electron configuration of the ions.
- For Cr$^{2+}$: We remove 2 electrons, first from the 4s orbital, then from the 3d orbital. The electron configuration is: \[ \text{Cr}^{2+}: [Ar] \, 3d^4 \] Number of 3d-electrons = (4)
- For Cu$^{2+}$: We remove 2 electrons, first from the 4s orbital, then from the 3d orbital. The electron configuration is: \[ \text{Cu}^{2+}: [Ar] \, 3d^9 \] Number of 3d-electrons = 9.
- For Ti$^{3+}$: We remove 3 electrons, first from the 4s orbital, then from the 3d orbital. The electron configuration is: \[ \text{Ti}^{3+}: [Ar] \, 3d^1 \] Number of 3d-electrons = (1)
- For Mn$^{2+}$: We remove 2 electrons, first from the 4s orbital, then from the 3d orbital. The electron configuration is: \[ \text{Mn}^{2+}: [Ar] \, 3d^5 \] Number of 3d-electrons = 5.
Step 3: Arranging in increasing order of 3d-electrons.
- Ti$^{3+}$ has 1 3d-electron.
- Mn$^{2+}$ has 5 3d-electrons.
- Cr$^{2+}$ has 4 3d-electrons.
- Cu$^{2+}$ has 9 3d-electrons.
Thus, the increasing order of 3d-electrons is:
Ti$^{3+}$ (1)<Mn$^{2+}$ (5)<Cr$^{2+}$ (4)<Cu$^{2+}$ (9).
Final Answer: \[ \boxed{\text{The correct order is (C), (D), (A), (B).}} \]