`Al` and `Ga` are trivalent in their compounds but monovalent compounds are the most stable down the `13th` group. Why?

Explanation

To understand why aluminum (Al) and gallium (Ga) are trivalent in their compounds but their monovalent compounds are the most stable down the 13th group, we can break down the explanation into a series of steps:

### Step-by-Step Solution:

1. **Identify the Group and Elements**:
The elements in the 13th group of the periodic table are Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl).

2. **Electronic Configuration**:
...