Question

Explain the meaning of inner transition series?

Answer 1

Periodic table consists of chemical elements in blocks. There are four blocks namely s, p, d, and f blocks in the periodic table. f-block elements are also known as inner transition elements as they were a part of d-block elements but placed at the bottom of the periodic table which gives the name as inner transition elements.

Complete answer:
Periodic table is the representation of chemical elements in the increasing order of atomic numbers. The periodic table was divided into four namely s, p, d, and f blocks in the periodic table. s-block consists of two groups, p-block consists of the last eight groups, d-block consists of three series and it is the block that was placed in the middle of s and p blocks. f-block elements are placed at the down of the periodic table.
As f-block elements are a part of d-block elements, as the last electron is entering into f-block, these elements are specially arranged at the bottom of the periodic table and known as inner transition series.
This inner transition series consists of two series namely lanthanide and actinide series. Lanthanides are the chemical elements from atomic number $59$ to $71$ and actinides are the chemical elements from atomic number $90$ to $103$ .

Note:
In the inner transition series the last electron enters into the f-orbital. f-orbital can accommodate $14$ electrons. Thus, the two inner transition series i.e., lanthanides and actinides have $14$ elements in each series. Actinides are mostly radioactive elements.