In the group of diatomic elements, which of the following is NOT included?

• A. Hydrogen
• B. Nitrogen
• C. Oxygen
• D. Xenon

Answer: (D)

Diatomic elements are molecules that consist of two atoms of the same element, typically existing as gases under standard conditions. Examples of diatomic elements include nitrogen (N2), hydrogen (H2), and oxygen (O2), all of which naturally occur as diatomic molecules in the atmosphere.

Xenon, however, is a noble gas and exists as single atoms (monatomic) rather than forming diatomic molecules. Noble gases, including xenon, have complete outer electron shells, which generally make them chemically inert and unlikely to bond with themselves or other elements to form diatomic molecules.

Hence, the correct answer indicates that xenon is not a diatomic element, distinguishing it from hydrogen, nitrogen, and oxygen, all of which are indeed diatomic gases in their natural form.