Question

In what periods are the lanthanides and actinides? Where are they
placed in the periodic table? Why?

Answer 1

Lanthanides are in period 6 and actinides are in period 7. They are at the down part of the page so that the periodic table can fit on the page.

Answer 2

Answer: They are palced in 6th and 7th period below the periodic table due to their properties and to keep the balanced shape of periodic table.