Which of the following diatomic molecules is held together by a nonpolar covalent bond, with the bonding electrons shared equally between identical atoms?

Introduction / Context:
Covalent bonds can be classified as polar or nonpolar depending on how equally the bonding electrons are shared between the bonded atoms. When two identical atoms share electrons, the electronegativity difference between them is zero, so the bond is nonpolar. Recognising which molecules have nonpolar covalent bonds is important for predicting physical properties such as solubility and boiling point. This question asks which diatomic molecules are held together by nonpolar covalent bonds.

Given Data / Assumptions:
- The molecules listed are Cl2, Br2 and H2, along with options that generalise about all of them or none of them.
- Each of these is a homonuclear diatomic molecule, meaning both atoms in the molecule are the same element.
- Electronegativity values for identical atoms are equal, leading to zero electronegativity difference.
- We assume basic valence bond descriptions of diatomic molecules in introductory chemistry.

Concept / Approach:
A nonpolar covalent bond occurs when the electrons in the bond are shared equally because the bonded atoms have the same electronegativity. In homonuclear diatomic molecules such as H2, Cl2 and Br2, the bonding electrons are shared equally between the two identical atoms. Therefore, the single covalent bond in each of these molecules is nonpolar. In contrast, polar covalent bonds form between atoms of different elements with different electronegativities, such as hydrogen and chlorine in HCl. Since all three molecules listed consist of identical atoms, they each contain nonpolar covalent bonds.

Step-by-Step Solution:
Step 1: Identify that H2 consists of two hydrogen atoms sharing a pair of electrons in a single covalent bond. Step 2: Recognise that Cl2 consists of two chlorine atoms, again with a shared electron pair forming a single covalent bond. Step 3: Note that Br2 consists of two bromine atoms sharing a pair of electrons in a similar way. Step 4: Understand that in each case, both atoms have the same electronegativity, so there is no electronegativity difference across the bond. Step 5: Conclude that all three bonds are nonpolar covalent bonds, so the correct choice is that all of the above molecules contain nonpolar covalent bonds.

Verification / Alternative check:
Textbooks often explain polarity by introducing homonuclear diatomic molecules as clear examples of nonpolar covalent bonding. Diagrams show symmetric electron density between the two identical atoms, indicating equal sharing. In contrast, examples of polar covalent bonds use molecules such as HCl, HF or H2O, where electrons are drawn more strongly toward one atom. The classification of H2, Cl2 and Br2 as nonpolar covalent is a standard part of this explanation, reinforcing the idea that all these molecules fall into the same nonpolar category.

Why Other Options Are Wrong:
Options A, B and C each identify only one specific molecule. Although each of those individual choices describes a molecule that does contain a nonpolar covalent bond, they ignore the fact that the other listed molecules also fit the same description. Option E states that none of these molecules have nonpolar covalent bonds, which contradicts basic bond polarity rules for homonuclear diatomics. The most complete and correct statement is captured by option D, which recognises that all of the listed molecules share electrons equally between identical atoms.

Common Pitfalls:
Students sometimes assume that any molecule containing halogens must have polar bonds, because halogens are highly electronegative. This is true when halogens bond with less electronegative elements, but not when they bond with themselves. Another pitfall is to equate colour or physical state with polarity, for example thinking that the colour of chlorine or bromine must relate to polar bonds. Polarity is determined by electronegativity difference, not by colour. Remembering that identical atoms form nonpolar covalent bonds helps avoid these confusions.

Final Answer:
All three diatomic molecules listed are held together by nonpolar covalent bonds, so the correct choice is All of the above.