3-Chlorobut-1-ene is solvolysed in water through a free allylic cation. Counting every stereoisomer that can in principle form (E/Z isomers and enantiomers counted separately), the number of different alcohols produced is

The cation $\mathrm{CH}{}_3-\mathrm{CH}{}^{+}-\mathrm{CH}=\mathrm{CH}{}_2\leftrightarrow \mathrm{CH}{}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}{}_2{}^{+}$ is attacked at either terminus. Attack at C-2 gives but-3-en-2-ol, which has one stereocentre: (R) and (S), 2 isomers. Attack at C-4 gives but-2-en-1-ol, with a C=C that can be E or Z: 2 isomers. Total $2+2=4$ stereoisomeric alcohols.