Which of the following is an example of a molecular compound?

A molecular compound is typically formed when two or more nonmetals share electrons through covalent bonds. In this case, H2O, or water, is a classic example of a molecular compound because it consists of two hydrogen atoms covalently bonded to one oxygen atom. The sharing of electrons between hydrogen and oxygen leads to the formation of a distinct molecular structure, characterized by the bonding and arrangements of these atoms.

The other compounds listed are ionic compounds. NaCl (sodium chloride), Fe2O3 (iron(III) oxide), and MgO (magnesium oxide) are formed from the electrostatic attraction between positively charged cations and negatively charged anions. These compounds do not consist of discrete molecules but rather exist as a lattice of ions, which is different from the molecular structure found in H2O. This distinction is key in identifying H2O as the molecular compound in this context.