The correct answer is option 'D', Lanthanum. The lanthanide series is a group of chemical elements that includes the 15 elements with atomic numbers 57 to 71. These elements are also known as the lanthanides or rare earth elements.

The lanthanide series starts with Lanthanum, which has an atomic number of 57. It is the first element in the series and serves as a representative for the rest of the elements in the series. Lanthanum is a soft, silvery-white metal and is commonly found in minerals such as monazite and bastnasite.

Now, let's discuss some key points about the lanthanide series:

1. Atomic Numbers: The lanthanide series includes the elements with atomic numbers 57 to 71. These elements are placed in the sixth period of the periodic table.

2. Similar Properties: The elements in the lanthanide series have similar chemical and physical properties. They are all metallic elements and have high melting and boiling points. They also tend to form stable 3+ ions.

3. Electron Configurations: The lanthanide elements have a common electron configuration in their outermost energy level, which is (n-2)f^n(n-1)d^1ns^2. This common electron configuration is responsible for their similar chemical properties.

4. Lanthanide Contraction: The lanthanide contraction refers to the decrease in size of the lanthanide elements as you move from left to right across the series. This phenomenon is due to the poor shielding effect of the 4f electrons.

5. Applications: The lanthanide elements have a wide range of applications. They are used in the production of magnets, phosphors for lighting and displays, catalysts, and in various other industries.

In conclusion, the lanthanide series starts with Lanthanum, which is the first element with an atomic number of 57. The lanthanide series includes the elements with atomic numbers 57 to 71 and they exhibit similar chemical and physical properties.