The correct order of stability for the following alkoxides is:

Alkoxide ions carry a negative charge on the oxygen atom ($$-\text{O}^\ominus$$). Their stability is enhanced by electron-withdrawing groups via resonance (mesomeric effect, $$-M$$) and induction ($$-I$$), which help delocalize the negative charge.

• Structure (C):

  The negative charge on the oxygen atom is in direct conjugation with the double bond and the nitro group ($$-\text{CH}=\text{CH}--\text{NO}_2$$). This allows the negative charge to be highly delocalized throughout the system by both resonance ($$-M$$) and inductive ($$-I$$) effects, making it the most stable alkoxide.

• Structure (B):

  The nitro group is attached to an $$sp^2$$ hybridized carbon atom of an isolated double bond. While it cannot delocalize the oxygen's lone pairs directly through extended resonance, it exerts a strong resonance effect on the alkene system alongside its strong inductive ($$-I$$) pull, providing intermediate stability.

• Structure (A):

  The nitro group is attached to a saturated $$sp^3$$ carbon atom. There is no resonance or conjugation possible for the nitro group here; it stabilizes the negative charge purely through the inductive effect ($$-I$$ only), which weakens significantly with distance. Hence, it is the least stable.