`NO_(2)` group is an electron-withdrawing group. Hence, it shows –I effect. By withdrawing the electrons toward it, the `NO_(2)` group decreases the negative charge on the compound, thereby stabilising it. On the other hand, ethyl group is an electron-releasing group. Hence, the ethyl group shows +I effect. This increases the negative charge on the compound, thereby destabilising it. Hence, `O_(2)NCH_(2)CH_(2)O^(–)` is expected to be more stable than `CH_(3)CH_(2)O^(-)`.
