Elements in the first period have valence electrons in

Options

A. N shell
B. K shell
C. M shell
D. S shell

Answer

To determine where the valence electrons of elements in the first period are located, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Elements in the First Period:**
- The first period of the periodic table contains two elements: Hydrogen (H) and Helium (He).

2. **Determine the Atomic Numbers:**
- Hydrogen has an atomic number of 1, and Helium has an atomic number of 2.

3. **Identify the Electron Configuration:**
- For Hydrogen (atomic number 1), it has 1 electron. This electron is in the first shell, known as the K shell.
- For Helium (atomic number 2), it has 2 electrons. Both of these electrons are also in the K shell.

4. **Define Valence Electrons:**
- Valence electrons are the electrons that are involved in chemical bonding. They are located in the outermost shell of an atom.

5. **Conclusion:**
- Since both Hydrogen and Helium have their valence electrons in the K shell, we can conclude that the elements in the first period have their valence electrons in the K shell.

### Final Answer:
Elements in the first period have valence electrons in the K shell.

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