Which of the following elements is a diatomic molecule?

RRB Nsg. Superintendent-20 July 2019 (Shift-2)

Biochemistry and Nutrition

Easy

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-2)

Explanation

Hydrogen exists as a diatomic molecule (H₂) under standard conditions.
A hydrogen atom has one valence electron and needs one more to achieve a stable electron configuration, similar to the noble gas Helium.
To achieve stability, two hydrogen atoms share their electrons to form a single covalent bond, resulting in a stable H₂ molecule.
A helpful mnemonic for the seven common diatomic elements is 'Have No Fear Of Ice Cold Beer': Hydrogen (H₂), Nitrogen (N₂), Fluorine (F₂), Oxygen (O₂), Iodine (I₂), Chlorine (Cl₂), Bromine (Br₂).

Option A: Sulphur is a polyatomic molecule, not diatomic. In its most common elemental form, it exists as an octatomic molecule (S₈), with eight atoms arranged in a puckered ring.
Option B: Argon is a noble gas. Its atoms have a full outer electron shell, making it very stable and chemically inert. Therefore, it exists as individual, unbonded atoms, which is described as monatomic.
Option C: Like Argon, Helium is a noble gas. Its atoms have a complete first electron shell (2 electrons), making it extremely stable and non-reactive. It exists as single atoms (monatomic).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Molecularity of Elements (Diatomic, Monatomic, Polyatomic) as background academic context rather than a clinical decision trigger.
Understanding the molecular nature of elements is fundamental to chemistry, which underpins pharmacology and physiology.
The diatomic nature of Oxygen (O₂) is critical for its role in cellular respiration. The monatomic nature of Helium (He) contributes to its low density, making it useful in specialized gas mixtures (heliox) to ease breathing in patients with respiratory obstruction.
What if? If the question asked for a diatomic gas that is a halogen, the answer could be Fluorine (F₂) or Chlorine (Cl₂), both of which are highly reactive and have specific industrial and medical applications (e.g., in disinfectants).

How to Approach the Question

First, identify the key term in the question: 'diatomic molecule'.
Define 'diatomic molecule': An element that naturally exists as a stable molecule containing two atoms bonded together.
Systematically evaluate each option based on this definition.
Recall or deduce that Helium and Argon are noble gases, which are famously stable as single atoms (monatomic). This eliminates them as answers.
Consider Sulphur. Recall that it forms larger, more complex structures, most commonly the S₈ ring, making it polyatomic.
This leaves Hydrogen. Recall that a single hydrogen atom is unstable and readily bonds with another hydrogen atom to form the stable H₂ molecule, which fits the definition of diatomic.

Concept Tested & Keywords

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