The acidity (Brønsted acidity) order of the following is

1. Compare $\mathrm{pK_a}$ values (lower $\mathrm{pK_a}$ = stronger acid). 2. PHENOL ($\mathrm{C_6H_5OH}$): $\mathrm{pK_a} \approx 10$. The phenoxide anion $\mathrm{C_6H_5O^-}$ is stabilised by RESONANCE — the negative charge delocalises onto the ortho/para ring positions. So phenol is comparatively acidic. 3. WATER ($\mathrm{H_2O}$): $\mathrm{pK_a} = 15.7$. The conjugate base $\mathrm{OH^-}$ is stabilised only by solvation, not resonance. 4. ETHANOL ($\mathrm{CH_3CH_2OH}$): $\mathrm{pK_a} \approx 16$. The ethoxide anion has the negative charge LOCALISED on a single oxygen, AND there's a destabilising electron-donating alkyl group ($\mathrm{+I}$) — so ethanol is the LEAST acidic. 5. Order of acidity: PHENOL > WATER > ETHANOL. 6. Option A reverses the order. Option B is half-reversed. Option D ignores the resonance effect. _Source: syllabus Chemistry Part 2, Ch 7, §7.4 (Acidity of alcohols and phenols), p. 10–11 + p. 15._