Which order of the rate of E2 elimination with $\mathrm{NaOEt}$ in ethanol is correct for $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}(\mathrm{X})\mathrm{CH}{}_3$ (same base and temperature)?

The rate follows the leaving-group ability, set by C-X bond strength and stability of the departing anion: iodide $>$ bromide $>$ chloride, and fluoride is by far the worst. So $\mathrm{X}=\mathrm{I}>\mathrm{Br}>\mathrm{Cl}>\mathrm{F}$.