The metal oxides that are acidic oxides are: vanadium pentoxide, chromium trioxide (chromic anhydride), tungsten trioxide, molybdenum trioxide, manganese heptaoxide, rhenium heptaoxide, osmium tetroxide, tin dioxide, antimony, bismuth pentaoxide and so on.
Neither acidic nor basic: iron tetraoxide, manganese dioxide, lead tetraoxide, vanadium dioxide and so on.