Why lanthanoids and actinoids are called f-block elements?

Explanation

### Step-by-Step Solution:

1. **Understanding the Position in the Periodic Table**:
- The lanthanoids and actinoids are located in the two rows that are placed below the main body of the periodic table. These rows are known as the lanthanide series and the actinide series, respectively.

2. **Identifying the Electron Configuration**:
- The key characteristic of these elements is that their last electrons are being added to the f-orbital. The f-orbitals are a specific type of atomic orbital that can hold a maximum of 14 electrons.

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