On heating with concentrated $\mathrm{H}{}_2\mathrm{SO}{}_4$, 2-methylbutan-2-ol gives mainly

Dehydration goes through the tertiary carbocation and follows Saytzeff's rule, giving the more substituted (more stable) alkene. Loss of H from the $\mathrm{CH}{}_2$ carbon gives the trisubstituted 2-methylbut-2-ene, which is favoured over the disubstituted 2-methylbut-1-ene.