Decreasing order of number of ionisable hydrogen atoms in the following molecules is I. $\mathrm{H}_3 \mathrm{PO}_4$ II. $\mathrm{H}_3 \mathrm{PO}_3$ III. $\mathrm{H}_3 \mathrm{PO}_2$ IV. $\mathrm{H}_4 \mathrm{P}_2 \mathrm{O}_6$

• A

  II $>$ IV $>$ I $>$ III
• B

  IV $>$ III $>$ II $>$ I
• Correct answer
  C

  IV $>$ I $>$ II $>$ III
• D

  II $>$ IV $>$ III $>$ I

Solution

Therefore, decreasing order of ionisable hydrogen. $\mathrm{H}_4 \mathrm{P}_2 \mathrm{O}_6>\mathrm{H}_3 \mathrm{PO}_4>\mathrm{H}_3 \mathrm{PO}_3>\mathrm{H}_3 \mathrm{PO}_2$ IV $>$ I $>$ II $>$ III

Hence, the correct answer is option: 'C'.