Phosphoric 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 K is the overall ionization constant. Which of the following statements are true?

A. \(\log K=\log {K}_{{a}_{1}}+\log {K}_{{a}_{2}}+\log {K}_{{a}_{3}}\)
B. \({\mathrm{H}}_{3}{\mathrm{PO}}_{4}\) is a stronger acid than \({\mathrm{H}}_{2}{\mathrm{PO}}_{4}^{-}\)and \({\mathrm{HPO}}_{4}^{2-}\)

\(\mathrm{C}.{\mathrm{K}}_{{\mathrm{a}}_{1}}>{\mathrm{K}}_{{\mathrm{a}}_{2}}>{\mathrm{K}}_{{\mathrm{a}}_{3}}\\ \mathrm{D}.{\mathrm{K}}_{{\mathrm{a}}_{1}}=\frac{{\mathrm{K}}_{{\mathrm{a}}_{3}}+{\mathrm{K}}_{{\mathrm{a}}_{2}}}{2}\)

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[NEET 2025]

Question

Phosphoric 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 K is the overall ionization constant. Which of the following statements are true?

A. \(\log K=\log {K}_{{a}_{1}}+\log {K}_{{a}_{2}}+\log {K}_{{a}_{3}}\)
B. \({\mathrm{H}}_{3}{\mathrm{PO}}_{4}\) is a stronger acid than \({\mathrm{H}}_{2}{\mathrm{PO}}_{4}^{-}\)and \({\mathrm{HPO}}_{4}^{2-}\)

\(\mathrm{C}.{\mathrm{K}}_{{\mathrm{a}}_{1}}>{\mathrm{K}}_{{\mathrm{a}}_{2}}>{\mathrm{K}}_{{\mathrm{a}}_{3}}\\ \mathrm{D}.{\mathrm{K}}_{{\mathrm{a}}_{1}}=\frac{{\mathrm{K}}_{{\mathrm{a}}_{3}}+{\mathrm{K}}_{{\mathrm{a}}_{2}}}{2}\)

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[NEET 2025]

YESPYQ · Accepted Answer

Correct answer: b) A, B and C only. Statement A: Total ionization constant K = Ka 1 × Ka 2 × Ka 3 Taking log on both sides: log K = log Ka 1 + log Ka 2 + log Ka 3 Statement A is correct Statement B: The first ionization of H 3 PO 4 is the greatest, so it is a stronger acid than H 2 PO 4 - and HPO 4 2- Statement B is correct Statement C: For polyprotic acids: Ka 1 > Ka 2 > Ka 3 Because removal of each successive proton becomes more difficult Statement C is correct Statement D: Ka 1 = (Ka 3 + Ka 2 ) / 2 No such general relation exists Statement D is incorrect

Phosphoric acid ionizes in three steps with their ionization constant values \({\mathrm{K}}_{{\mathrm{a}}_{1}},{\mathrm{…

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