The maximum COVALENCY of Boron is 4 where as that of Al is 6 . The order of EN of IIIA group ELEMENTS is `B gt Al lt Ga lt In lt TI` Down the group the oxidising power increases . The ordder of acidic NATURE : `N_(2)O_(3) gt P_(2) O_(3) gt As_(2) O_(3) gt Sb_(2)O_(3) gt Bi_(2)O_(3)`