Question

Lanthanoide series (15 elements) starts from which of the following element?

• A. Actinium (Ac)
• B. Cerium (Ce)
• C. Lanthanum (La)
• D. Thorium (Th)

Hint:

Counting 15 elements from atomic number 57 gives the series.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
When the lanthanoids are counted as 15 elements, they run from Z = 57 to Z = 71. The series is named after its first member.

Step 2: Identify the first member
Element 57 is lanthanum (La) and element 71 is lutetium (Lu).

Step 3: Compare the options
Ac and Th belong to the actinoid series. Ce (Z = 58) is the second member. So La is the start.

Final Answer:
The series starts with lanthanum (La). \[ \boxed{\text{(C) }\text{Lanthanum (La)}} \]