The acidity ($K_a$) order for the carboxylic acids $\mathrm{HCOOH}$ (formic), $\mathrm{CH_3COOH}$ (acetic), and $\mathrm{CICH_2COOH}$ (chloroacetic) is

1. NCERT §8.6 (Carboxylic Acids — acidity): an ELECTRON-WITHDRAWING substituent on the $\alpha$-carbon stabilises the conjugate base (carboxylate), increasing acidity. 2. Chloroacetic acid: $\mathrm{Cl}$ is strongly electron-withdrawing by INDUCTION. Stabilises $\mathrm{ClCH_2COO^-}$ → most acidic. $K_a \approx 1.3\times 10^{-3}$. 3. Formic acid: $\mathrm{H}$ on the $\alpha$-position. No alkyl group to donate electrons → moderately acidic. $K_a \approx 1.8\times 10^{-4}$. 4. Acetic acid: $\mathrm{CH_3}$ is electron-DONATING (hyperconjugation/induction), destabilises the carboxylate → least acidic. $K_a \approx 1.8\times 10^{-5}$. 5. Order: $\mathrm{ClCH_2COOH} > \mathrm{HCOOH} > \mathrm{CH_3COOH}$, matching option C. 6. Other options reverse one or more entries — common confusion between '$\mathrm{CH_3}$ donates' vs '$\mathrm{CH_3}$ withdraws'. _Source: NCERT Class 12 Chemistry Part 2, Ch 8, §8.6 (Carboxylic Acids — acidity, effect of substituents) + Table 8.4, p. 18–19._