The ether shown is treated with one equivalent of $\mathrm{HI}$ and the resulting alkyl iodide is isolated and heated with alcoholic $\mathrm{KOH}$. Which structure is the major alkene formed?

The ether is tert-pentyl methyl ether. Its tertiary alkyl group ionises, so cleavage by $\mathrm{HI}$ gives 2-iodo-2-methylbutane and methanol. Alcoholic $\mathrm{KOH}$ then causes E2 elimination, following Saytzeff's rule, which gives the more substituted alkene, 2-methylbut-2-ene. The alcohol is a substitution product, and 2-methylbut-1-ene is the minor (Hofmann) alkene.