When ${\mathrm{NaH}}_2{\mathrm{PO}}_4$ is heated then which of the   following compound is formed?

 

A derivative called sodium dihydrogen phosphate is formed by reacting mono- and diglycerides from edible sources with phosphorus pentoxide and then neutralizing the reaction with sodium carbonate.

As sodium hydrogen phosphate is heated, it first transforms into sodium pyrophosphate and then sodium metaphosphate.

$2{\mathrm{Na}}_2{\mathrm{PO}}_4\to {\mathrm{Na}}_4{\mathrm{P}}_2{\mathrm{O}}_7\to {\mathrm{Na}}_4{\mathrm{P}}_2{\mathrm{O}}_7+{\mathrm{H}}_2\mathrm{O}$

${\mathrm{Na}}_4{\mathrm{P}}_2{\mathrm{O}}_7\to 2{\mathrm{NaPO}}_3+{\mathrm{Na}}_2\mathrm{O}\stackrel{{\mathrm{H}}_2\mathrm{O}}{\to }2\mathrm{NaOH}$

Hence, option B is correct.