How is a secondary alcohol defined?

A secondary alcohol is defined by the presence of the hydroxyl group (-OH) attached to a carbon atom that is itself bonded to two other carbon atoms, which inherently means it must have only one hydrogen atom attached to it. In a secondary alcohol, the structure allows for the carbon holding the hydroxyl to be linked to two other carbons, making it central within the molecular framework.

This definition is critical, as it delineates secondary alcohols from primary and tertiary alcohols. In primary alcohols, the carbon with the hydroxyl group is attached to only one other carbon and has two hydrogen atoms, while in tertiary alcohols, the carbon with the hydroxyl group is attached to three other carbons and does not have any hydrogen atoms.

Thus, the defining characteristic of a secondary alcohol hinges on the attachment of the hydroxyl group to a carbon with exactly one hydrogen atom, affirming the correct choice in this context.