Question

lanthanides and actinides comes into which group and which period

Answer 1

The two rows that are generally placed underneath the main Periodic Table are called the lanthanide series and the actinide series. These two rows are produced when electrons are being added to f orbitals. Therefore, this block of elements are referred to as the "f block".

Answer 2

These are f block elements. Starting from 6th and 7th period, these elements starts from 3rd group.