Which of the following is not representative element?1. Tellurium2. Tantalum3. Thallium4. Astatine

To determine which of the given elements is not a representative element, we need to understand what representative elements are. Representative elements are the elements in the periodic table that belong to the s and p blocks. These elements are also known as the main group elements.

1. Tellurium: Tellurium belongs to the p block and is a representative element.
2. Tantalum: Tantalum belongs to the d block and is not a representative element.
3. Thallium: Thallium belongs to the p block and is a representative element.
4. Astatine: Astatine belongs to the p block and is a representative element.

Therefore, the element that is not a representative element is Tantalum (option 2).