What are lanthanides and actinides?

Answer: Lanthanides and actinides are belong to f -block of the periodic table.

Elements 58 to 71 in the lanthanide series finally fill their 4f sublevel. The elements 89 to 103 that make up the actinides  fill their 5f sublevel. 

The 15 naturally occurring metallic chemical elements known as lanthanides have atomic numbers that range from 57 (lanthanum) to 71. (Lutetium).  These have a wide range of applications in both science and industry.

Actinide series, which consists of elements with atomic numbers ranging from 89 to 103. The series can be found on the row of the periodic table that is beneath the Lanthanide series.

The general electronic configuration of f– block: (n-2) f^(0-14) (0-14) (n-1) d^(0-2) ns²