Explanation:
Firstly, we need to define primary, a secondary, and tertiary alcohol
Primary alcohol: A primary alcohol in which the hydroxyl group is bonded to a primary carbon atom. Examples of primary alcohol are ethanol and 1-butanol.
The structure of a primary alcohol is given below
Secondary alcohol: A secondary alcohol has the hydroxyl group on a secondary carbon atom, which is bonded to two other carbon atoms.
Examples of secondary alcohol are propan-2-ol, butan-2-ol, pen-3-ol
The structure of a secondary alcohol is given below
Tertiary alcohol: Tertiary alcohol is a compound in which a hydroxy group, -OH, is attached to a saturated carbon atom which has three other carbon atoms attached to it.
Examples of tertiary alcohol are 2-methylpropan-2-ol, 2-methylbutan-2-ol
The structure of tertiary alcohol is given below
According to the question given,
The first structure has a single alkyl group and the functional group(OH) is attached to the primary atom. Hence, Butan-ol is a primary alcohol.
The second structure has two alkyl groups and the function group is on the second carbon atom. Hence, it belongs to the secondary alcohol group.
The third structure belongs to tertiary alcohol