\(-\mathrm{OH}\) (hydroxyl groups).
\(C_{n} H_{2 n+2} (Alkanes) \xrightarrow[{ + OH}]{{ - H}} C_{n} H_{2 n+1} O H\) or \(C_{n} H_{2 n+2} O\)

$(i)$ $C{H_3}C{H_2}C{H_2}C{H_3}$
$(ii)$ $C{H_3} - CH = CH - C{H_3}$
$(iii)$ $C{H_2} = CH - CH = C{H_2}$
$(iv)$ $H - C \equiv C - H$