Why the `f`-block elements are called inner transition elements?

Explanation

### Step-by-Step Solution:

1. **Definition of f-block Elements**: The f-block elements consist of two series: the lanthanides and actinides. These elements are characterized by the filling of f-orbitals with electrons.

2. **Position in the Periodic Table**: The f-block elements are located at the bottom of the periodic table, separate from the main body of the table. This positioning is significant because it indicates that they are not part of the main groups (s, p, d-blocks) of the periodic table.

3. **Inner Transition Elements**: The term "inner transition elements" refers to the fact that these f-block elements transition between the s and d-block elements. They are called "inner" because they are located in the inner part of the periodic table, as opposed to the outer transition elements (the d-block).

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