2-Bromobutane is heated with $\mathrm{KOH}$ in ethanol. The major alkene is:

Saytzeff's rule: the more substituted (more stable) alkene predominates. Removal of H from C3 gives disubstituted but-2-ene, while removal from C1 gives monosubstituted but-1-ene (minor). Butanol would be a substitution product, not an alkene.