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Chemistry · PYQ NEET UG 2025
हिन्दीPhosphoric acid ionizes in three steps with their ionization constant values \( \mathrm{K}_{\mathrm{a}_1}, \mathrm{K}_{\mathrm{a}_2} \) and \( \mathrm{K}_{\mathrm{a}_3} \), respectively, while \( \mathrm{K} \) is the overall ionization constant. Which of the following statements are true? A. \( \log \mathrm{K} = \log \mathrm{K}_{\mathrm{a}_1} + \log \mathrm{K}_{\mathrm{a}_2} + \log \mathrm{K}_{\mathrm{a}_3} \) B. \( \mathrm{H}_3\mathrm{PO}_4 \) is a stronger acid than \( \mathrm{H}_2\mathrm{PO}_4^- \) and \( \mathrm{HPO}_4^{2-} \). C. \( \mathrm{K}_{\mathrm{a}_1} > \mathrm{K}_{\mathrm{a}_2} > \mathrm{K}_{\mathrm{a}_3} \) D. \( \mathrm{K}_{\mathrm{a}} = \frac{\mathrm{K}_{\mathrm{a}_3} + \mathrm{K}_{\mathrm{a}_2}}{2} \) Choose the correct answer from the options given below:
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Correct answer · Option D
A, B and C only
Explanation
Overall equilibrium constant \( K = K_{a1} \times K_{a2} \times K_{a3} \), taking log gives A. Acid strength decreases with successive dissociation, so \( K_{a1} > K_{a2} > K_{a3} \) (C) and \( \mathrm{H}_3\mathrm{PO}_4 \) is strongest (B). Statement D is incorrect.
