In the following brown complex, the oxidation state of iron is + \ \ \ \. [ Fe ( H_2 O )_6]^2++ NO → Brown complex [ Fe ( H_2 O )_5( NO )]^2+ + H_2 O

In the following brown complex, the oxidation state of iron is + \_\_\_\_. $$\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}+\mathrm{NO} \rightarrow \underset{\text { Brown complex }}{\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_5(\mathrm{NO})\right]^{2+}}+\mathrm{H}_2 \mathrm{O} $$