The PHENOXIDE ion is more STABLE than the ethoxide ion because

1. Phenol's conjugate base, the phenoxide $\mathrm{C_6H_5O^-}$, has 4 important resonance structures: one with the negative charge on O, and three with the charge on the ortho/para ring carbons. 2. RESONANCE DELOCALISATION lowers the energy of the phenoxide ion, making it more STABLE. 3. Ethoxide $\mathrm{CH_3CH_2O^-}$ has NO such resonance — the negative charge is LOCALISED entirely on the single O atom. 4. More stable conjugate base means STRONGER parent acid: this is why phenol ($\mathrm{pK_a}\sim 10$) is much more acidic than ethanol ($\mathrm{pK_a}\sim 16$). 5. The electron-DONATING alkyl group in ethoxide ($\mathrm{+I}$ effect) further destabilises the negative charge — a separate factor reinforcing the same conclusion. 6. Options B–D have no chemical basis. _Source: NCERT Class 12 Chemistry Part 2, Ch 7, §7.4 (Acidity of phenol — resonance argument), p. 15._