the order of strength of acids is HIO < HIO2 < HIO3 IO3- > IO2- >IO- in IO4- iodine is bonded to 3 O\'s and one O- . Now, since O is electron withdrawing it decreses electron density on I more and more and makes the -ve charge stable... this effect decreases when you go to IO3- because there are only two O\'s and hence the order.. Solution the order of strength of acids is HIO < HIO2 < HIO3 IO3- > IO2- >IO- in IO4- iodine is bonded to 3 O\'s and one O- . Now, since O is electron withdrawing it decreses electron density on I more and more and makes the -ve charge stable... this effect decreases when you go to IO3- because there are only two O\'s and hence the order...