An ALCOHOL in which the $\mathrm{-OH}$ group is attached to a carbon bonded to ONE other alkyl group is classified as

1. syllabus classifies alcohols by the substitution at the carbon bearing the $\mathrm{-OH}$ group. 2. PRIMARY (1°): the $\mathrm{C{-}OH}$ carbon is attached to ONE other carbon (one alkyl group). Example: ethanol $\mathrm{CH_3CH_2OH}$. 3. SECONDARY (2°): attached to TWO other carbons. Example: propan-2-ol $\mathrm{(CH_3)_2CHOH}$. 4. TERTIARY (3°): attached to THREE other carbons. Example: $\mathrm{(CH_3)_3COH}$ (tert-butanol). 5. There is no QUATERNARY (4°) alcohol — that would require 4 carbons attached, leaving no room for $\mathrm{-OH}$. 6. Other options describe higher substitution patterns not matching the stated single-alkyl case. _Source: syllabus Chemistry Part 2, Ch 7 "Alcohols, Phenols and Ethers", §7.1.1 (Classification of alcohols), p. 1–2._