Which of the two: O₂NCH₂CH₂O^– or CH₃CH₂O^– is expected to be more stable and why?

NO₂ is the electron withdrawing group. Hence, it shows –I effect. By withdrawing the electrons toward it, the NO₂ group decreases the negative charge on the compound, thereby stabilising it, as as shown below:

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, O₂NCH₂CH₂O- is expected to be more stable than CH₂CH₂O^-.