Which of the following represents a primary alcohol?

A primary alcohol is characterized by the presence of an -OH (hydroxyl) group attached to a carbon atom that is only connected to one other carbon atom. In the context of the given structures, the correct representation of a primary alcohol is the one where the hydroxyl group is on a carbon that is only bonded to one other carbon.

In the chosen structure, CH3-CH2-OH, the hydroxyl group is attached to the second carbon (the ethyl part), which is itself attached to only one other carbon (the methyl part), confirming it is a primary alcohol. This aligns perfectly with the definition, as the carbon with the -OH group cannot be bonded to any additional carbon atoms aside from the one it is directly connected to.

The other choices depict structures where the carbon bearing the -OH group is bonded to more than one carbon, which qualifies them as secondary or tertiary alcohols rather than primary. A secondary alcohol would feature the hydroxyl group on a carbon that is attached to two other carbon atoms, while a tertiary alcohol would have the hydroxyl group on a carbon surrounded by three other carbons. Thus, the identification of CH3-CH2-OH as the primary alcohol is accurate because it meets all criteria