Which of the following has same number of electrons in the last shell?

Options

A. As and B
B. Sn and Pb
C. N and O
D. Fe and Cr

Explanation

To determine which of the given elements has the same number of electrons in their last shell (valence shell), we will analyze the valence electrons of each pair of elements provided in the question.

### Step-by-Step Solution:

1. **Identify the Elements:**
- The elements given are Arsenic (As), Boron (B), Tin (Sn), Lead (Pb), Nitrogen (N), Oxygen (O), Iron (Fe), and Chromium (Cr).

2. **Group Classification:**
- **Arsenic (As)**: Group 15 (5 valence electrons)
- **Boron (B)**: Group 13 (3 valence electrons)
- **Tin (Sn)**: Group 14 (4 valence electrons)
- **Lead (Pb)**: Group 14 (4 valence electrons)
- **Nitrogen (N)**: Group 15 (5 valence electrons)
- **Oxygen (O)**: Group 16 (6 valence electrons)
- **Iron (Fe)**: Transition metal (6 valence electrons)
- **Chromium (Cr)**: Transition metal (6 valence electrons)

3. **Compare the Valence Electrons:**
- **Arsenic (5) and Boron (3)**: Different number of valence electrons.
- **Tin (4) and Lead (4)**: Same number of valence electrons (4).
- **Nitrogen (5) and Oxygen (6)**: Different number of valence electrons.
- **Iron (6) and Chromium (6)**: Same number of valence electrons (6).

4. **Conclusion:**
- The pairs with the same number of electrons in the last shell are:
- Tin (Sn) and Lead (Pb) - both have 4 valence electrons.
- Iron (Fe) and Chromium (Cr) - both have 6 valence electrons.

5. **Final Answer:**
- The elements that have the same number of electrons in the last shell are **Tin (Sn) and Lead (Pb)**.