Which of the following pairs of elements have same number of electrons in their outermost shell?

Options

A. Mn, Fe
B. Na, Sr
C. As, Bi
D. Se, Te

Answer

To determine which pairs of elements have the same number of electrons in their outermost shell (valence electrons), we need to analyze the groups of the elements and their electron configurations. Here’s a step-by-step solution:

### Step 1: Identify the Elements and Their Groups
We need to identify the groups for each pair of elements provided in the question.

1. **Manganese (Mn)**: Group 7 (or Group 7B)
2. **Iron (Fe)**: Group 8 (or Group 8B)

3. **Sodium (Na)**: Group 1
4. **Strontium (Sr)**: Group 2

5. **Arsenic (As)**: Group 15 (or Group 5A)
6. **Bismuth (Bi)**: Group 15 (or Group 5A)

7. **Selenium (Se)**: Group 16 (or Group 6A)
8. **Tellurium (Te)**: Group 16 (or Group 6A)

### Step 2: Determine the Valence Electron Configuration
Next, we need to find the valence electron configurations for each element.

1. **Manganese (Mn)**:
- Electron Configuration: [Ar] 4s² 3d⁵
- Valence Electrons: 2 (from 4s) + 5 (from 3d) = 7

2. **Iron (Fe)**:
- Electron Configuration: [Ar] 4s² 3d⁶
- Valence Electrons: 2 (from 4s) + 6 (from 3d) = 8

3. **Sodium (Na)**:
- Electron Configuration: [Ne] 3s¹
- Valence Electrons: 1

4. **Strontium (Sr)**:
- Electron Configuration: [Kr] 5s²
- Valence Electrons: 2

5. **Arsenic (As)**:
- Electron Configuration: [Ar] 4s² 3d¹⁰ 4p³
- Valence Electrons: 2 (from 4s) + 3 (from 4p) = 5

6. **Bismuth (Bi)**:
- Electron Configuration: [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p³
- Valence Electrons: 2 (from 6s) + 3 (from 6p) = 5

7. **Selenium (Se)**:
- Electron Configuration: [Ar] 4s² 3d¹⁰ 4p⁴
- Valence Electrons: 2 (from 4s) + 4 (from 4p) = 6

8. **Tellurium (Te)**:
- Electron Configuration: [Kr] 5s² 4d¹⁰ 5p⁴
- Valence Electrons: 2 (from 5s) + 4 (from 5p) = 6

### Step 3: Compare the Valence Electrons
Now we compare the number of valence electrons for each pair:

1. **Manganese and Iron**: 7 vs 8 (Different)
2. **Sodium and Strontium**: 1 vs 2 (Different)
3. **Arsenic and Bismuth**: 5 vs 5 (Same)
4. **Selenium and Tellurium**: 6 vs 6 (Same)

### Conclusion
The pairs of elements that have the same number of electrons in their outermost shell are:
- **Arsenic (As) and Bismuth (Bi)**
- **Selenium (Se) and Tellurium (Te)**