The isomerism exhibited due to the difference in the size of the alkyl groups attached to the same functional group is

$\underset{\mathrm{Diethyl} \mathrm{ether}}{{\mathrm{C}}_2{\mathrm{H}}_5-\mathrm{O}-{\mathrm{C}}_2{\mathrm{H}}_5} ; \underset{\mathrm{Methyl} \mathrm{propyl} \mathrm{ether}}{{\mathrm{C}}_3{\mathrm{H}}_7-\mathrm{O}-{\mathrm{CH}}_3}$

In the above Ex. D.H in size of alkyl group attached to the same functional group.