Find total number of conditions in which oxidation of ${\mathrm{Fe}}^{+2}$(aq) ions to iron (III) takes palces :

(a) On exposure to air
(b) On addition to conc. ${\mathrm{HNO}}_3$
(c) On reaction with ${\mathrm{SnCl}}_2$
(d) On reaction with ${\mathrm{H}}_2{\mathrm{O}}_2$
(e) On reaction with ${\mathrm{MnO}}_4^{-}/{\mathrm{H}}^{+}$
(f) On reaction with $\mathrm{KI}$
(g) On reaction with ${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}/{\mathrm{H}}^{+}$