The transition element ( with few exceptions ) show a large number of oxidation states . The various oxidation states are related to the electronic configuration of their atoms. The variable oxidation states of a transition metal is due to the involvement of (n-1)d and outer ns electrons . For the first five elements of 3d transition series , the minimum oxidation state is equal to the number of electrons in 4s shell and the maximum oxidation state is equal to the sum of 4s and 3d electrons. The relative stability of various oxidation states of a given element can be explained on the basis of stability of `d^(0),d^(5) and d^(10)` configuration .
In which of the following pairs , the first species is more stable than second one

Options

A. `Ti^(3+),Ti^(4+)`
B. `Mn^(2+),Mn^(3+)`
C. `Fe^(2+),Fe^(3+)`
D. `Sc^(+2),Sc^(+3)`

Answer

To solve the problem of determining which of the given pairs has the first species more stable than the second, we will analyze the oxidation states and electronic configurations of the transition metals involved. The stability of oxidation states can be explained based on the stability of d^0, d^5, and d^10 configurations.

### Step-by-Step Solution:

1. **Understanding Oxidation States**:
- Transition metals can exhibit multiple oxidation states due to the involvement of (n-1)d and ns electrons.
- The minimum oxidation state corresponds to the number of electrons in the outermost 4s shell.
- The maximum oxidation state is the sum of the electrons in the 4s and (n-1)d orbitals.

2. **Stability of Electronic Configurations**:
- d^0 configuration (no d electrons) is stable.
- d^5 configuration (half-filled d subshell) is particularly stable due to symmetry and exchange energy.
- d^10 configuration (fully filled d subshell) is also stable.

3. **Analyzing Each Pair**:
- **Pair 1: Ti^3+ vs Ti^4+**
- Ti has the configuration 3d^2 4s^2.
- Ti^3+ has 3d^1 (removal of 2 electrons from 4s and 1 from 3d).
- Ti^4+ has 3d^0 (removal of all 4 electrons).
- **Stability**: Ti^4+ (d^0) is more stable than Ti^3+ (d^1). **Incorrect**.

- **Pair 2: Mn^2+ vs Mn^3+**
- Mn has the configuration 3d^5 4s^2.
- Mn^2+ has 3d^5 (removal of 2 electrons from 4s).
- Mn^3+ has 3d^4 (removal of 1 electron from 3d).
- **Stability**: Mn^2+ (d^5) is more stable than Mn^3+ (d^4). **Correct**.

- **Pair 3: Fe^2+ vs Fe^3+**
- Fe has the configuration 3d^6 4s^2.
- Fe^2+ has 3d^6 (removal of 2 electrons from 4s).
- Fe^3+ has 3d^5 (removal of 1 electron from 3d).
- **Stability**: Fe^3+ (d^5) is more stable than Fe^2+ (d^6). **Incorrect**.

- **Pair 4: Sc^2+ vs Sc^3+**
- Sc has the configuration 3d^1 4s^2.
- Sc^2+ has 3d^1 (removal of 2 electrons from 4s).
- Sc^3+ has 3d^0 (removal of all 3 electrons).
- **Stability**: Sc^3+ (d^0) is more stable than Sc^2+ (d^1). **Incorrect**.

4. **Conclusion**:
- The only pair where the first species is more stable than the second is Mn^2+ vs Mn^3+.

### Final Answer:
The correct pair where the first species is more stable than the second is **Mn^2+ and Mn^3+**.