For ${\mathrm{I}}_2+2\mathrm{e}\to 2{\mathrm{I}}^{-}$, standard reduction potential = + 0.54 volt. For $2{\mathrm{Br}}^{-}\to {\mathrm{Br}}_2+2{\mathrm{e}}^{-}$, standard oxidation potential = – 1.09 volt. For $\mathrm{Fe}\to {\mathrm{Fe}}^{2+}+2{\mathrm{e}}^{-}$standard oxidation potential = + 0.44 volt. Which of the following reactions is non-spontaneous?

A redox reaction in which SRP of oxidising agent is lesser than SRP of reducing agent is non-spontaneous and does not occurs. 

Alternatively, If E_cell comes to be negative the reaction is non-spontaneous and does not occur.

For option (4), E⁰= E⁰(Cathode)-E⁰(anode)= +0.54V-1.09V=-0.55V ;