The alkene shown is treated with (i) dilute aqueous $\mathrm{H}{}_2\mathrm{SO}{}_4$, then (ii) $\mathrm{PCC}$ in $\mathrm{CH}{}_2\mathrm{Cl}{}_2$. Which structure is the final organic product?

The alkene is 3-methylbut-1-ene. Acid hydration proceeds through a hydride shift to the tertiary cation and gives 2-methylbutan-2-ol. A tertiary alcohol has no H on the carbinol carbon and cannot be oxidised by $\mathrm{PCC}$, so it is recovered unchanged.