Final answer:
Diagram a represents calcium oxide (CaO) due to the depicted 2+ ion, indicating calcium's +2 charge. Diagram b represents sodium fluoride (NaF) with a 1+ ion, pointing to sodium's +1 charge.
Step-by-step explanation:
The diagrams refer to two ionic compounds, NaF and CaO. To determine which is which, we consider the ionic charges of the components of each compound. Sodium (Na) has an oxidation number of +1 and fluorine (F) has an oxidation number of -1, forming sodium fluoride (NaF) with a 1:1 ratio of Na+ to F-. For calcium oxide (CaO), calcium (Ca) has an oxidation number of +2, and oxygen (O) has an oxidation number of -2, forming a 1:1 ratio of Ca2+ to O2-. Given the diagrams, diagram a, showing a 2+ ion and diagram b showing a 1+ ion, it can be deduced that diagram a represents calcium oxide (CaO) because calcium has a +2 charge, and diagram b represents sodium fluoride (NaF) because sodium has a +1 charge.