How many elements are present in the lanthanide series of the periodic table?

• A. 10
• B. 7
• C. 14
• D. 15

Answer: (D)

Verified step by step guidance

1. Understand that the lanthanide series consists of elements in the periodic table where the 4f orbitals are being filled.
2. Identify the starting element of the lanthanide series, which is Lanthanum (La) with atomic number 57, and the ending element, which is Lutetium (Lu) with atomic number 71.
3. Count the number of elements from Lanthanum (57) to Lutetium (71) inclusive. This can be done by subtracting the atomic number of Lanthanum from that of Lutetium and then adding 1 to include both endpoints: \$71 - 57 + 1$.
4. Recognize that this count gives the total number of elements in the lanthanide series, which corresponds to the number of 4f electrons being filled.
5. Conclude that the lanthanide series contains 15 elements based on this counting method.