Chromium is a transition metal, and you should remember that some of these have electrons in their inner shells which can be used as valence electrons, which give them their variable oxidation states. Chromium can exist as +2, +3 or +6.
Some of these elements you mention are not typically tested due to their variable behavior.
for example, Cerium is especially interesting because of its variable electronic structure. The energy of the inner 4f level is nearly the same as that of the outer (valence) electrons, and only small amounts of energy are required to change the relative occupancy of these electronic levels. This gives rise to dual valence states.
For example, a volume change of about 10 percent occurs when cerium is subjected to high pressures or low temperatures. Cesium's valence appears to change from about 3 to 4 when it is cooled or compressed. The low temperature behavior of cerium is complex.
Hope this helps, good luck!
