Question

which of the following ionic compounds is incorrectly named?
ca3(po4)2, calcium phosphate
cu2s, copper(i) sulfide
fe2o3, iron(iii) oxide
(nh4)2so3, ammonium sulfite
pbo2, lead(ii) oxide

Explanation:

1. Analyze each compound - ion naming rules:

• For $Ca_3(PO_4)_2$, calcium has a +2 charge and phosphate ($PO_4^{3 -}$) is named correctly as calcium phosphate.
• For $Cu_2S$, copper in +1 oxidation state is named copper(I) sulfide correctly.
• For $Fe_2O_3$, iron in +3 oxidation state is named iron(III) oxide correctly.
• For $(NH_4)_2SO_3$, ammonium ($NH_4^+$) and sulfite ($SO_3^{2 -}$) are named ammonium sulfite correctly.
• For $PbO_2$, lead has a +4 oxidation - state in this compound, so it should be named lead(IV) oxide, not lead(II) oxide.

Answer:

E. $PbO_2$, lead(II) oxide