Which of the following elements is diatomic?

Step 1: Analyze the question The question asks which element exists as a diatomic molecule, meaning two atoms of the same element bonded together (formula X₂).

Step 2: The concept Only a few elements are diatomic under normal conditions. A handy list is the seven diatomic elements:

• Hydrogen (H₂)
• Nitrogen (N₂)
• Oxygen (O₂)
• Fluorine (F₂)
• Chlorine (Cl₂)
• Bromine (Br₂)
• Iodine (I₂)

Step 3: Check each option

• A. Sodium: a metal. It exists as a metallic lattice of Na atoms and is not diatomic.
• B. Oxygen: exists as O₂, with a double bond between two oxygen atoms. This is diatomic.
• C. Iron: a metal with a giant metallic structure, so it is not diatomic.
• D. Neon: a noble gas with a full outer shell. It exists as single atoms (monatomic), so it is not diatomic.

Step 4: Answer

Exam tip: Remember the diatomic elements with the phrase "HONClBrIF" (pronounced "Hon-cl-brif"). Also remember that metals are never diatomic and noble gases (He, Ne, Ar, and so on) are monatomic.