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JEE Main levelSingle correct optionDifficulty 2 of 3co191

Given pKa values: p-methoxybenzoic acid 4.47, p-toluic acid 4.37, benzoic acid 4.20, p-nitrobenzoic acid 3.44. The correct order of increasing acid strength is

  1. Abenzoic < p-methoxybenzoic < p-toluic < p-nitrobenzoic
  2. Bp-nitrobenzoic < benzoic < p-toluic < p-methoxybenzoic
  3. Cp-toluic < p-methoxybenzoic < benzoic < p-nitrobenzoic
  4. Dp-methoxybenzoic < p-toluic < benzoic < p-nitrobenzoic

Answer: D

Larger pKa means weaker acid. In increasing acidity the pKa values fall: 4.47 > 4.37 > 4.20 > 3.44. Electron-donating groups (, ) destabilise the anion and the nitro group stabilises it.
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