What are transition elements ? Why are they so called ? Name the different transition series.

Explanation

### Step-by-Step Solution:

1. **Definition of Transition Elements**:
Transition elements are defined as the d-block elements that are found in groups 3 to 12 of the periodic table. These elements are characterized by the presence of d electrons in their penultimate shell.

2. **Reason for the Name "Transition Elements"**:
They are called transition elements because they exhibit properties that are intermediate between the s-block and p-block elements. Their position in the periodic table is between these two blocks, and they show transitional behavior in their chemical properties and oxidation states.

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