Dehydration of alcohols involves the formation of carbocation intermediates. More the stability of carbocation, more will be the ease of alcohol towards dehydration.
$ \because $ The order of stability of carbocations is
$ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, 3^\circ > 2^\circ > 1^\circ $
$ \therefore $ The order of ease of dehydration of alcohols is
$ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, 3^\circ > 2^\circ > 1^\circ $