Which of the following oxy-acids has the maximum number of hydrogens directly attached to phosphorus?

Which of the following oxy-acids has the maximum number of hydrogens directly attached to phosphorus?
  1. $\mathrm{H}_{4} \mathrm{P}_{2} \mathrm{O}_{7}$
  2. $\mathrm{H}_{3} \mathrm{PO}_{2}$
  3. $\mathrm{H}_{3} \mathrm{PO}_{3}$
  4. $\mathrm{H}_{3} \mathrm{PO}_{4}$

Asked in: JEE-TOPICTESTS-CHEMISTRY

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