Arrange the following elements in decreasing order of metallic character:
`K, Mg, B, Al`.

Explanation

To arrange the elements K (Potassium), Mg (Magnesium), B (Boron), and Al (Aluminum) in decreasing order of metallic character, we can follow these steps:

### Step 1: Understand Metallic Character
Metallic character refers to the tendency of an element to lose electrons and form positive ions (cations). The more readily an element can lose electrons, the more metallic it is.

### Step 2: Periodic Trends
- **Left to Right Across a Period**: Metallic character decreases. This means that elements on the left side of the periodic table are more metallic than those on the right.
- **Top to Bottom in a Group**: Metallic character increases. This means that as you move down a group in the periodic table, the elements become more metallic.
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