AIIMS 2017 Chemistry Chromium Compounds MCQ Question

The reaction between Cr₂O₇²⁻ and OH⁻ to form CrO₄²⁻ is classified as an acid-base reaction because it involves the transfer of protons (H⁺) in a basic medium, where Cr₂O₇²⁻ acts as an acid and OH⁻ as a base. In contrast, the other options are incorrect: it is not a redox reaction since there is no change in oxidation states, nor is it a precipitation reaction as no insoluble compound is formed, and it does not involve complexation, which requires the formation of coordination complexes. This highlights the importance of recognizing the nature of chemical interactions in determining the type of reaction.