The rate of the E1 (ionisation) reaction of 2-chloro-2-methylpropane is expected to be highest in which solvent?

The slow step creates charge separation, so the rate rises with the ionising power (polarity and hydrogen-bond donation) of the solvent. A water-rich aqueous ethanol solvates both the carbocation and chloride best, whereas acetone and ether stabilise ions poorly and hexane not at all.