Question

4 a student correctly identifies fecl₂ and fecl₃ as ionic compounds but gives them different names. which explanation best justifies why the names are different? a iron can form more than one oxidation state, which must be indicated in the name. b the compounds have different numbers of valence electrons. c ionic compounds require prefixes when more than two atoms are present. d chlorine changes its charge depending on the compound.

Explanation:

• Option A: Iron (Fe) is a transition metal that can have multiple oxidation states (e.g., +2 in $\ce{FeCl2}$ and +3 in $\ce{FeCl3}$). When naming ionic compounds with metals having variable oxidation states, the oxidation state (charge) of the metal must be indicated in the name (using Roman numerals), which explains the different names for $\ce{FeCl2}$ (iron(II) chloride) and $\ce{FeCl3}$ (iron(III) chloride).
• Option B: The number of valence electrons of the compounds is not the reason for different naming; naming depends on ion charges/oxidation states.
• Option C: Ionic compounds (with metals and non - metals) do not use prefixes for naming; prefixes are used in covalent (molecular) compound naming (e.g., $\ce{CO2}$ - carbon dioxide).
• Option D: Chlorine in ionic compounds with metals (like in these iron chlorides) has a fixed charge of - 1 (as $\ce{Cl^-}$), so it does not change its charge depending on the compound.

Answer:

A. Iron can form more than one oxidation state, which must be indicated in the name.