Question

Why 4f and 5f inner transition series of elements are placed separately in the periodic table?

Answer 1

Because if you put lanthanides and actinides in to the Periodic Table like transition metals, the table will be way too wide. The two rows of elements present at thebottom of the periodic table are called the 4f series or lanthanoids and 5f or actanoids. They are also called inner transition elements.