Final answer:
Among the options NaCl, AlCl₃, MgBr₂, and H₂, H₂ is a molecule, specifically a diatomic molecule consisting of two hydrogen atoms. Option D is correct.
Step-by-step explanation:
The student has asked which compound among the listed options is a molecule. A molecule is defined as a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.
Among the given options, H₂ is a molecule because it consists of two hydrogen atoms bonded covalently. Options A) NaCl, B) AlCl₃, and C) MgBr₂ are ionic compounds, not molecules, as they are composed of cations and anions held together by ionic bonds.
To clarify with examples from the provided information, sodium chloride (NaCl) is an ionic compound composed of sodium cations (Na+) and chloride anions (Cl⁻) in a crystal lattice structure. Similarly, magnesium bromide (MgBr₂) is formed by magnesium cations (Mg²⁺) and bromide anions (Br⁻) with a 1:2 ratio to balance the charges. In contrast, elemental hydrogen (H₂) is a diatomic molecule, comprising two hydrogen atoms bonded together, thus forming a molecule.