The correct answer would be, Element.
The gas used to fill party balloons contains only Helium atoms. This makes Helium an element.
Explanation:
Helium is a Chemical Element. It has a symbol of He. It has an atomic number 2. Helium is a gas which is colorless, odorless, non toxic, etc, in nature.
In Chemistry, when a substance has all the atoms having same atomic number, or same number of protons, the substance is considered as an Element.
So when all party balloons are filled with the Helium gas only, the atomic number or the number of protons of the substance becomes same, which make the Helium gas, an Element.
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