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 understand the stability of the Gd^(3+) ion, we can break down the reasoning into a few clear steps:

### Step 1: Determine the Electronic Configuration of Gadolinium
Gadolinium (Gd) has the atomic number 64. Its ground state electronic configuration is:
- **Xe** (the configuration of xenon) followed by **4f^7 5d^1 6s^2**.

### Step 2: Identify the Electronic Configuration of Gd^(3+)
When Gadolinium loses three electrons to form the Gd^(3+) ion, the electrons are removed from the outermost shells first. The electrons are removed in the following order:
1. The two electrons from the 6s subshell.
2. One electron from the 5d subshell.

Thus, the electronic configuration of Gd^(3+) becomes:
- **Xe 4f^7**.

### Step 3: Analyze the 4f^7 Configuration
The 4f subshell can hold a maximum of 14 electrons. The configuration 4f^7 means that there are 7 electrons in the 4f subshell. This configuration is significant because:
- The 4f subshell is not completely filled (which would be 4f^14) and is also not empty (which would be 4f^0).
- A half-filled subshell (like 4f^7) tends to be more stable due to symmetry and exchange energy considerations.

### Step 4: Conclusion on Stability
The stability of the Gd^(3+) ion can be attributed to the half-filled nature of the 4f subshell. The presence of 7 electrons in the 4f subshell provides extra stability due to:
- Exchange energy, which is maximized in half-filled and fully filled subshells.
- Symmetrical distribution of electrons.

Therefore, the reason for the stability of the Gd^(3+) ion is that the 4f subshell is half-filled.

### Final Answer
The stability of the Gd^(3+) ion is due to the half-filled 4f^7 subshell, which provides extra stability.

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