Final answer:
The lanthanides and actinides are placed separately at the bottom of the periodic table as part of the inner transition metals. This arrangement maintains the compact form of the periodic table while emphasizing their unique properties.
Step-by-step explanation:
The lanthanides and actinides are placed in two separate rows at the bottom of the periodic table because they are both part of the inner transition metals. These elements have unique electronic configurations and exhibit similar chemical properties. Placing them separately helps to maintain the periodic table's compact form, while also highlighting their similarities and distinguishing them from the other elements.
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