On moving horizontally across a period, the number of electrons in the outermost shell increases from - to -,

Options

A. 2,8
B. 2,18
C. 1,8
D. 1,18

Answer

To answer the question, "On moving horizontally across a period, the number of electrons in the outermost shell increases from - to -," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Periodic Table**:
- The periodic table is organized into periods (horizontal rows) and groups (vertical columns). Each period corresponds to the filling of a new electron shell.

2. **Identifying the Elements in a Period**:
- Let's consider the second period of the periodic table, which includes the elements: Lithium (Li), Beryllium (Be), Boron (B), Carbon (C), Nitrogen (N), Oxygen (O), Fluorine (F), and Neon (Ne).

3. **Counting Valence Electrons**:
- As we move from left to right across a period, the number of valence electrons (the electrons in the outermost shell) increases.
- For example:
- Lithium (Li) has 1 valence electron.
- Beryllium (Be) has 2 valence electrons.
- Boron (B) has 3 valence electrons.
- Carbon (C) has 4 valence electrons.
- Nitrogen (N) has 5 valence electrons.
- Oxygen (O) has 6 valence electrons.
- Fluorine (F) has 7 valence electrons.
- Neon (Ne) has 8 valence electrons.

4. **Conclusion**:
- Therefore, as we move from Lithium (1 valence electron) to Neon (8 valence electrons), we see that the number of electrons in the outermost shell increases from 1 to 8.

### Final Answer:
On moving horizontally across a period, the number of electrons in the outermost shell increases from **1 to 8**.

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