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ExamsJEE MainChemistry

Consider the following three reactions involving dihydrogen phosphate ion: (i) H3PO4 + H2O → H3O+ + H2PO4− (ii) H2PO4− + H2O → HPO4^2− + H3O+ (iii) H2PO4− + OH− → H3PO4 + O2− In which of these reactions does H2PO4− behave as an acid?

  1. (ii) only
  2. (i) and (ii)
  3. (iii) only
  4. (i) only

Correct answer: (i) only

Solution

In reaction (i), H2PO4− acts as a proton donor, releasing a proton to water and forming H3O+, which is characteristic of an acid. In contrast, in reactions (ii) and (iii), H2PO4− either accepts a proton or does not donate one, thus not behaving as an acid.

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