To analyze the assertion and reason provided in the question, we will follow these steps:
### Step 1: Determine the Electron Configuration of Neutral Iron (Fe)
The electron configuration of neutral iron (Fe) is:
\[ \text{Fe: } 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 3d^6 \]
### Step 2: Determine the Electron Configuration of Fe²⁺ Ion
When iron loses two electrons to form the Fe²⁺ ion, the two electrons are removed from the 4s orbital first, followed by the 3d orbital. The electron configuration for Fe²⁺ is:
\[ \text{Fe}^{2+}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 3d^6 \]
This means Fe²⁺ has 4 unpaired electrons in the 3d subshell.
### Step 3: Determine the Electron Configuration of Fe³⁺ Ion
When iron loses one more electron to form the Fe³⁺ ion, it removes one electron from the 3d subshell. The electron configuration for Fe³⁺ is:
\[ \text{Fe}^{3+}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 3d^5 \]
This means Fe³⁺ has 5 unpaired electrons in the 3d subshell.
### Step 4: Compare Stability of Fe²⁺ and Fe³⁺
The assertion states that Fe³⁺ is more stable than Fe²⁺. The reason for this is that the Fe³⁺ ion has a half-filled d subshell (3d⁵), which is known to be more stable due to exchange energy and symmetry considerations. Thus, the assertion is true.
### Step 5: Evaluate the Reason
The reason given states that Fe³⁺ has more unpaired electrons than Fe²⁺. While this is true (Fe³⁺ has 5 unpaired electrons compared to Fe²⁺'s 4), the reason does not correctly explain the assertion. The stability of Fe³⁺ is primarily due to the half-filled d subshell rather than just the number of unpaired electrons.
### Conclusion
- **Assertion (A)**: True - Fe³⁺ is indeed more stable than Fe²⁺.
- **Reason (R)**: True - Fe³⁺ has more unpaired electrons than Fe²⁺, but it does not provide the correct explanation for the assertion.
Thus, the answer is that both the assertion and reason are true, but the reason is not the correct explanation for the assertion.
