How does the valency vary in going down a group?

Explanation

### Step-by-Step Solution:

1. **Understanding Valency**: Valency is defined as the ability of an atom to combine with other atoms, which is determined by the number of electrons in the outermost shell (valence electrons).

2. **Identifying Groups in the Periodic Table**: Elements in the same group of the periodic table have similar chemical properties because they have the same number of valence electrons. For example, Group 1 elements (alkali metals) all have one electron in their outermost shell.

3. **Example of Group 1 Elements**:
- **Lithium (Li)**: Atomic number 3, electronic configuration is 1s² 2s¹. It has 1 valence electron.
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