How many elements are present in the d-block of the periodic table?

Explanation

To determine how many elements are present in the d-block of the periodic table, we can follow these steps:

### Step 1: Identify the d-block Elements
The d-block elements are also known as transition metals. They are found in groups 3 to 12 of the periodic table.

### Step 2: Determine the Series of d-block Elements
The d-block contains four series of transition metals:
1. **3d series**: This series includes elements from atomic number 21 (Scandium) to 30 (Zinc).
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