Respuesta :
Answer:
Transition metals like Fe have multiple oxidation states and hence they need to be specified by roman numerals. In contrast, Ba is an alkali metal with a constant +2 oxidation state which need not be specified in the compound names.
Explanation:
Oxidation state of an element can be ascribed to the loss or gain of electrons. Metals in general are electropositive i.e. they tend to lose electrons and form cations.
Iron (Fe) is a transition metal and belongs to the 'd-block' within the periodic table. Transition metals are characterized by the presence of five d-orbitals that are partially filled with electrons of similar energies. Thus for d-block elements there are several electrons that can be removed which results in multiple oxidation states. In the case of Fe the most common oxidation states are +2 and +3. Therefore, for any given compound of iron it is imperative to specify its oxidation state. In this case the compound is Fe(NO3)2 where Fe is in the +2 oxidation state as represented by the roman numeral 'II', hence iron (II) nitrate.
Barium (Ba) in contrast is an alkaline earth metal with a single oxidation state of +2. Any compound of Ba will only exhibit a +2 oxidation state which is assumed to be the case and therefore not explicitly specified, hence Ba(NO3)2 is called barium nitrate and not barium (II) nitrate.
