Which of the following do not have the same number of valence electrons?

Options

A. H, Li, Na, K
B. He, Mg, Be, Ca
C. B, AI, N, P
D. O, S, Se

Explanation

To determine which of the given options does not have the same number of valence electrons, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Option A: Hydrogen, Lithium, Sodium, Potassium**
- **Hydrogen (H)**: Atomic number = 1, Electronic configuration = 1. Valence electrons = 1.
- **Lithium (Li)**: Atomic number = 3, Electronic configuration = 2,1. Valence electrons = 1.
- **Sodium (Na)**: Atomic number = 11, Electronic configuration = 2,8,1. Valence electrons = 1.
- **Potassium (K)**: Atomic number = 19, Electronic configuration = 2,8,8,1. Valence electrons = 1.
- **Conclusion for Option A**: All have 1 valence electron. So, they have the same number of valence electrons.

2. **Option B: Helium, Magnesium, Beryllium, Calcium**
- **Helium (He)**: Atomic number = 2, Electronic configuration = 2. Valence electrons = 2.
- **Magnesium (Mg)**: Atomic number = 12, Electronic configuration = 2,8,2. Valence electrons = 2.
- **Beryllium (Be)**: Atomic number = 4, Electronic configuration = 2,2. Valence electrons = 2.
- **Calcium (Ca)**: Atomic number = 20, Electronic configuration = 2,8,8,2. Valence electrons = 2.
- **Conclusion for Option B**: All have 2 valence electrons. So, they have the same number of valence electrons.

3. **Option C: Boron, Aluminium, Nitrogen, Phosphorus**
- **Boron (B)**: Atomic number = 5, Electronic configuration = 2,3. Valence electrons = 3.
- **Aluminium (Al)**: Atomic number = 13, Electronic configuration = 2,8,3. Valence electrons = 3.
- **Nitrogen (N)**: Atomic number = 7, Electronic configuration = 2,5. Valence electrons = 5.
- **Phosphorus (P)**: Atomic number = 15, Electronic configuration = 2,8,5. Valence electrons = 5.
- **Conclusion for Option C**: Boron and Aluminium have 3 valence electrons, while Nitrogen and Phosphorus have 5 valence electrons. Thus, they do not have the same number of valence electrons.

4. **Option D: Oxygen, Sulphur, Selenium**
- **Oxygen (O)**: Atomic number = 8, Electronic configuration = 2,6. Valence electrons = 6.
- **Sulphur (S)**: Atomic number = 16, Electronic configuration = 2,8,6. Valence electrons = 6.
- **Selenium (Se)**: Atomic number = 34, Electronic configuration = 2,8,18,6. Valence electrons = 6.
- **Conclusion for Option D**: All have 6 valence electrons. So, they have the same number of valence electrons.

### Final Conclusion:
The option that does not have the same number of valence electrons is **Option C: Boron, Aluminium, Nitrogen, and Phosphorus**.

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