Which one of the following is a tertiary alcohol?

The correct answer is option 3.

Primary, secondary, and tertiary alcohols are classified based on the carbon atom to which the hydroxyl group \(-OH\) is attached. Here’s a detailed explanation:

Primary Alcohols (1° Alcohols)

In primary alcohols, the carbon atom that carries the \(-OH\) group is attached to only one other alkyl group (or none if it's methanol) and two hydrogen atoms.

General Formula: \(RCH_2OH\), where \(R\) is an alkyl group.

Examples: Methanol \(CH_3OH\), Ethanol \(CH_3CH_2OH\), 1-Butanol \(CH_3CH_2CH_2CH_2OH\), etc..

Secondary Alcohols (2° Alcohols)

In secondary alcohols, the carbon atom that carries the \(-OH\) group is attached to two other alkyl groups and one hydrogen atom.

General Formula: \(R_2CHOH\), where \(R\) can be the same or different alkyl groups.

Examples: Isopropanol \(CH_3CHOHCH_3\), 2-Butanol \(CH_3CH_2CHOHCH_3\), Cyclohexanol \(C_6H_{11}OH\) (the hydroxyl group is attached to a carbon in the cyclohexane ring), etc..

Tertiary Alcohols (3° Alcohols)

In tertiary alcohols, the carbon atom that carries the \(-OH\) group is attached to three other alkyl groups and no hydrogen atoms.

General Formula: \(R_3COH\), where \(R\) can be the same or different alkyl groups.

Examples: tert-Butanol (2-Methyl-2-propanol) \(C(CH_3)_3OH\), 2-Methyl-2-butanol \(CH_3CH_2C(CH_3)_2OH\), 2-Methyl-2-pentanol \(CH_3CH_2CH_2C(CH_3)_2OH\), etc..

Based on the information, the compounds given in options can be classified as: