When the outer electron shell is full in an element, this creates a

When the outer electron shell is full in an element, this creates a Noble gas.

Explanation:

Noble gases are the elements that belong to group 18 in the periodic table.  Noble gases are also called as inert gases. The outermost shell of the noble gases are fully filled by electrons. Due to this the noble gases don’t react with any other elements and remain isolated.

There are 6 noble gases in the periodic table. They are helium (He), Argon (Ar), Neon (Ne) Krypton (Kr), Radon (Rn) and Xenon (Xe). Noble gases conduct electricity. They are fluorescent, odorless and colorless. Noble gases are used a maintain stable elements in a constant and safe environment.

the answer is c) an oak tree