What i know about the above question is that a compound acts as an oxidising as well as reducing agent when the oxidation of central metal is somewhere between it's maximum and minimum oxidation state which is in the case for $NaNO_2,NaNO$.I don't know how to choose between the two.Any more information about the behaviour of other two compounds will be helpful.Thank you
I agree with Ivan Neretin in that the sodium oxidation state is equal in all compounds, and it will not act as oxidizing or reducing agent.
Na$_2$O will not act as a strong oxidizing or reducing agent, as both ions are in their preferred state.
NaO$_3$, or sodium ozonide, will likely act as an oxidative agent. However, I believe it disproportionates in water: 4 O$_3$ $^-$ + 2 H$_2$O $\rightarrow$ 5 O$_2$ + 4 OH$^-$, so that's kind of a candidate: it goes from oxidation state -1/3 to 0 and -II.
NaNO also seems strange to me - if it's Na$_2$N$_2$O$_2$, I see here that it acts as a reducing agent.
NaNO$_2$ can certainly act as both reducing and oxidizing agent, as the nitrogen atom is in oxidation state +III.
In conclusion, (4) seems to be the safest bet, considering only one answer is expected.