Question

what are lanthanides and actinides ?

Answer 1

Lanthanide elemdnt are nothing but they are elements with atomic number increasing from 57 to 71. They are termed Lanthanide because the lighter elements in the series are chemically similar to lanthanum. Actinides in the sense the radioactivite decay of uranium produces transmit amounts actinium and protactinium and atoms of neptunium etc.

Answer 2

These both are elements in the periodic table.
Lanthanides are elements with atomic numbers from 57 - 71.They are also called rare earths.These are elements in the row beginning with lanthanum.
Actinides  are elements with atomic number 89-103.