$\begin{array}{ccc}\mathrm{P}+\underset{\mathrm{hot} \mathrm{and} \mathrm{concentrated}}{{\mathrm{HNO}}_3}& \to & \mathrm{X}+{\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O}\\ 2\mathrm{X}& \stackrel{-{\mathrm{H}}_2\mathrm{O}}{\to }& \mathrm{Y}\end{array}$

Identified the hybridization of phosphorous in compound Y.

Reaction of P with concentrated with HNO₃ is:

$\mathrm{P}+\underset{\mathrm{hot} \mathrm{and} \mathrm{concentrated}}{5{\mathrm{HNO}}_3}\to 5{\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O}+\underset{\mathrm{X}}{{\mathrm{H}}_3{\mathrm{PO}}_4}$

Compound forms when one water is removed from 2 moles of X is:

$\underset{\mathrm{X}}{2{\mathrm{H}}_3{\mathrm{PO}}_4}\to {\mathrm{H}}_6{\mathrm{P}}_2{\mathrm{O}}_8\stackrel{-{\mathrm{H}}_2\mathrm{O}}{\to }\underset{\mathrm{Y}}{{\mathrm{H}}_4{\mathrm{P}}_2{\mathrm{O}}_7}$

Structure of H₄P₂O₇ is:

P is sp³ hybridized because it forms four sigma bonds, one with terminal oxygen atom, two sigma bonds with two -OH groups and one with the bridge O atom.