There are 14 elements that belong to the lanthanide series.

Explanation:
The lanthanide series is a group of chemical elements that have similar properties and belong to the f-block of the periodic table. These elements are also known as the rare earth elements.

The lanthanide series starts with the element lanthanum (symbol La) and ends with the element lutetium (symbol Lu). Therefore, there are 14 elements in total that belong to this series.

Here is a list of the elements in the lanthanide series:
1. Lanthanum (La)
2. Cerium (Ce)
3. Praseodymium (Pr)
4. Neodymium (Nd)
5. Promethium (Pm)
6. Samarium (Sm)
7. Europium (Eu)
8. Gadolinium (Gd)
9. Terbium (Tb)
10. Dysprosium (Dy)
11. Holmium (Ho)
12. Erbium (Er)
13. Thulium (Tm)
14. Lutetium (Lu)

These elements have similar properties because they all have the same number of valence electrons, which determines their chemical behavior. The lanthanide series elements are also known for their characteristic colors and their ability to form stable complexes with other elements.

Overall, there are 14 elements in the lanthanide series, which range from lanthanum to lutetium.