The reason for the stability of `Gd^(3-)` ion is

Options

A. 4f subshell - half filled
B. 4f subshell - completely filled
C. Possesses the general electronic configuration of noble gases.
D. 4f - subshell empty

Explanation

To determine the reason for the stability of the Gd^(3+) ion, we can follow these steps:

### Step 1: Identify the Element and Its Atomic Number
Gadolinium (Gd) is the element in question, and it has an atomic number of 64.

### Step 2: Write the Electronic Configuration
The electronic configuration of Gadolinium can be written as:
\[ \text{Gd: } [Xe] 4f^7 5d^1 6s^2 \]
This indicates that Gadolinium has 7 electrons in the 4f subshell, 1 electron in the 5d subshell, and 2 electrons in the 6s subshell.

### Step 3: Determine the Oxidation State
When Gadolinium loses 3 electrons to form the Gd^(3+) ion, it loses the 2 electrons from the 6s subshell and 1 electron from the 5d subshell. The electronic configuration of Gd^(3+) becomes:
\[ \text{Gd}^{3+}: [Xe] 4f^7 \]
This means that the 4f subshell now has 7 electrons.

### Step 4: Analyze the Stability of the 4f Subshell
The stability of electron configurations is influenced by the filling of subshells. A half-filled subshell (like 4f^7) is generally more stable due to symmetry and exchange energy. In this case, the 4f subshell is not fully filled, but it is half-filled, which is a stable configuration.

### Step 5: Conclusion
The stability of the Gd^(3+) ion is primarily due to the fact that it achieves a half-filled 4f subshell configuration after losing 3 electrons. This half-filled configuration is energetically favorable and contributes to the stability of the ion.

### Final Answer
The reason for the stability of the Gd^(3+) ion is that it has a half-filled 4f subshell after losing 3 electrons.

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