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JEE Main levelOne or more correct optionsDifficulty 2 of 3g2026

The pKa values of acetic acid and benzoic acid are 4.76 and 4.20. Which of the following statements are correct?

  1. AFormic acid is a stronger acid than acetic acid because the methyl group of acetic acid destabilises the acetate ion by its +I effect and hyperconjugation.
  2. BTrichloroacetic acid is a stronger acid than dichloroacetic acid.
  3. C4-Nitrobenzoic acid is a stronger acid than benzoic acid.
  4. DBenzoic acid is a weaker acid than acetic acid.

Answer: A, B, C

Formic acid has H instead of an electron-donating CH3, so its anion is better stabilised (pKa 3.75 against 4.76). Three chlorines withdraw electrons more than two, and a para nitro group stabilises the benzoate. Statement 4 is false because benzoic acid (pKa 4.20) is stronger than acetic acid (4.76), the sp2 carbon of the ring being more electron withdrawing than CH3.
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