No.of Lanthanides/Actinides - 14 Or 15?
Q

Whether the Lanthanide series consists of 14 or 15 elements is somewhat debatable.

Ans:

Lanthanide means "like lanthanum". So strictly speaking lanthanum (La) should not be considered as a Lanthanide. But based on common usage IUPAC acknowledges lanthanum as a Lanthanide. We shall therefore stick to Lanthanide series as having 15 elements from lanthanum(atomic no.57) to lutetium (atomic no.71)

Similarly, actinum(Atomic no. 89) shall also be considered as an element of Actinides series.