## Chemistry and Chemical Reactivity (9th Edition)

A) No changes in the oxidation numbers. B) Changes in the oxidation number: $Ca/CaO$: $Ca :0\rightarrow+2$ $O_2/CaO$: $O:0\rightarrow-2$ C) Changes in the oxidation number: $Fe(OH)_2/Fe(OH)_3$: $Fe :+2\rightarrow+3$ $O_2/Fe(OH)_3$: $O:0\rightarrow-2$