Which of the following is an example of a structural formula?

A structural formula provides a visual representation of the arrangement of atoms within a molecule, showing how the atoms are bonded together. In this context, HCHO represents formaldehyde, which is a simple chemical compound with a carbon atom double-bonded to an oxygen atom and single-bonded to a hydrogen atom and an aldehyde hydrogen.

The structural formula is particularly useful for understanding the specific connections between atoms and the geometry of the molecule. HCHO clearly indicates the arrangement and type of bonds in the molecule, which is essential for discussing reactivity, polarity, and intermolecular forces.

Other choices present chemical formulas that convey the number of atoms of each element but do not provide specific information on how these atoms are connected. C2H4 (ethylene) is a molecular formula that shows two carbon and four hydrogen atoms but lacks detail about their arrangement. CH3OH (methanol), while it gives the number of atoms, is also typically represented in a way that does not fully illustrate the bonds. RCHO indicates a generic structure for aldehydes but does not provide specific atomic arrangements. Thus, HCHO stands out as the only option that reflects a clear structural formula representation.