${\mathrm{HNO}}_3+{\mathrm{P}}_4{\mathrm{O}}_{10}⟶{\mathrm{HPO}}_3+\mathrm{A}$; the product is A.

Dinitrogen pentoxide and phosphoric acids are created when phosphorus pentoxide and nitric acid combine. Dinitrogen pentoxide manufacturing process. At a temperature of -10°, this reaction occurs.

$$\begin{gathered} 4{\mathrm{HNO}}_3+{\mathrm{P}}_4{\mathrm{O}}_{10}\to 4{\mathrm{HPO}}_3+\underset{\text{ nitrogen pentaoxide }}{{\mathrm{N}}_2{\mathrm{O}}_5} \\ \text{ (X)} \end{gathered}$$