On the basis of trends in the properties of the `3d`-series elements , suggested possible `M^(2+)` aqua ions for use as reducing agents , and write a balanced chemical equation for the reaction of one of those ions with `O_(2)` in acidic solution.

Explanation

Because oxidation `+2` is most stable for the later element of `3d` -series reducing agent include ions of the metals on the left of the series . Such ions include `V^(2+)`(aq) The `Fe^(2+)` (aq) ions is only weakly . The `CO^(2+) (aq)Ni^(2+)(aq)`, and `CU^(2+)(aq)` ions are not oxidized in water
`Fe^(3+ )undersetto(+0.77)
Fe^(2+) undersetto(-0.44) Fe`

The chemical equation for the oxidation is then
`4Fe^(2+)(aq)+O_(2)(g)+4H^(+)(aq)to4Fe^(3+)(aq)+2H_(2)O(l)`