Which belongs to the actinide series?

Concept:

• Our periodic table as given by Moseley and has in total 7 periods running horizontally and 18 groups running vertically.
• They are also further divided into s, p, d, and f blocks depending on the placement of the outermost electrons.
• Elements belonging to the same blocks resemble in their chemical and physical properties.
• The s block elements lie in the 1st and 2nd group.
• The p block elements belong to groups 13-18.
• The d and f block elements lie in the middle from group number 3-12.

Explanation:

• Actinides are the elements whose atomic number is from 90 to 103.
• The members of the series are Thorium, Protactinium, Uranium, Neptunium, Plutonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, Mendelevium, Nobelium, Lawrencium.
• Ce is Cerium which is not an actinide. Ca is calcium and Cs is Cesium, both are not actinides.

Hence, the actinide is Cf; Californium.