Which one of the following first series of transition elements has 5 unpaired electron in its+2 oxidation state?

Options

A. Mn(25)
B. Co(27)
C. V(23)
D. Cr(24)

Answer

To determine which first series transition element has 5 unpaired electrons in its +2 oxidation state, we will analyze the electron configurations of the relevant transition elements.

### Step 1: Identify the relevant transition elements
The first series of transition elements includes:
- Scandium (Sc, atomic number 21)
- Titanium (Ti, atomic number 22)
- Vanadium (V, atomic number 23)
- Chromium (Cr, atomic number 24)
- Manganese (Mn, atomic number 25)
- Iron (Fe, atomic number 26)
- Cobalt (Co, atomic number 27)
- Nickel (Ni, atomic number 28)
- Copper (Cu, atomic number 29)
- Zinc (Zn, atomic number 30)

### Step 2: Write the electron configurations of the relevant elements
1. **Manganese (Mn, atomic number 25)**:
- Ground state: [Ar] 4s² 3d⁵
- +2 oxidation state: [Ar] 3d⁵ (removing 2 electrons from 4s)

2. **Cobalt (Co, atomic number 27)**:
- Ground state: [Ar] 4s² 3d⁷
- +2 oxidation state: [Ar] 3d⁷ (removing 2 electrons from 4s)

3. **Vanadium (V, atomic number 23)**:
- Ground state: [Ar] 4s² 3d³
- +2 oxidation state: [Ar] 3d³ (removing 2 electrons from 4s)

4. **Chromium (Cr, atomic number 24)**:
- Ground state: [Ar] 4s¹ 3d⁵ (due to half-filled stability)
- +2 oxidation state: [Ar] 3d⁴ (removing 1 electron from 4s and 1 from 3d)

### Step 3: Determine the number of unpaired electrons in the +2 oxidation states
- **Mn²⁺**: [Ar] 3d⁵ → 5 unpaired electrons (all 5 d orbitals are singly occupied)
- **Co²⁺**: [Ar] 3d⁷ → 3 unpaired electrons (3 electrons in separate orbitals and 2 paired)
- **V²⁺**: [Ar] 3d³ → 3 unpaired electrons (3 electrons in separate orbitals)
- **Cr²⁺**: [Ar] 3d⁴ → 4 unpaired electrons (4 electrons in separate orbitals)

### Conclusion
The element that has 5 unpaired electrons in its +2 oxidation state is **Manganese (Mn)**.

### Summary of Steps:
1. Identify the transition elements.
2. Write their electron configurations in the ground state and +2 oxidation state.
3. Count the number of unpaired electrons in the +2 oxidation state.