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The correct order of decreasing acid strength of trichloroacetic acid (A), trifluoroacetic acid (B), acetic acid (C) and formic acid (D) is:
A
A > C > B > D
B
B > A > D > C
C
B > D > C > A
D
A > B > C > D
Detailed Solution
Electron-withdrawing groups (–I effect) stabilise the carboxylate ion and increase acid strength; electron-releasing groups (+I) decrease it.
F is more electronegative than Cl, so $CF_3COOH > CCl_3COOH$.
The $CH_3$ group in acetic acid has a +I effect, so HCOOH > $CH_3COOH$.
Order: $CF_3COOH$ (B) > $CCl_3COOH$ (A) > HCOOH (D) > $CH_3COOH$ (C)
F is more electronegative than Cl, so $CF_3COOH > CCl_3COOH$.
The $CH_3$ group in acetic acid has a +I effect, so HCOOH > $CH_3COOH$.
Order: $CF_3COOH$ (B) > $CCl_3COOH$ (A) > HCOOH (D) > $CH_3COOH$ (C)