For the redox reaction $x{\mathrm{P}}_4+y{\mathrm{HNO}}_3⟶{\mathrm{H}}_3{\mathrm{PO}}_4+{\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O}$

Reduction of Half- reaction :

${\mathrm{H}}^{+}+{\mathrm{HNO}}_3+e^{-}\to {\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O}$

Oxidation of Half reaction :

${\mathrm{P}}_4^{\ast }+16{\mathrm{H}}_2\mathrm{O}\to 4{\mathrm{H}}_3{\mathrm{PO}}_4+20{\mathrm{H}}^{+}+20{\mathrm{e}}^{-}$

The balanced chemical equation is mentioned below:-

Overall reaction: ${\mathrm{P}}_4+20{\mathrm{HNO}}_3\to 4{\mathrm{H}}_3{\mathrm{PO}}_4+20{\mathrm{NO}}_2+4{\mathrm{H}}_2\mathrm{O}$

So, For the redox reaction ${\mathrm{xP}}_4+{\mathrm{yHNO}}_3\to 4{\mathrm{H}}_3{\mathrm{PO}}_4+20{\mathrm{NO}}_2+4{\mathrm{H}}_2\mathrm{O}$ is x = 1, and y = 20.