Which one of the following oxides of nitrogen is known as ‘anhydride’ of nitric acid ?

Dinitrogen pentoxide (N2O5) is identified as the anhydride of nitric acid (HNO3). An acid anhydride is a compound that reacts with water to form an oxyacid; specifically, the hydration of N2O5 yields nitric acid (N2O5 + H2O → 2HNO3). It can be produced by the dehydration of nitric acid using phosphorus(V) oxide. In contrast, dinitrogen trioxide (N2O3) is the anhydride of nitrous acid (HNO2), while nitrogen dioxide (NO2) reacts with water to form a mixture of both nitric and nitrous acids. N2O5 is unique among nitrogen oxides as it exists as a colorless crystalline solid at room temperature, behaving as an ionic species (nitronium nitrate) in its solid state and a covalent molecule in its gaseous phase. Its role as a nitric anhydride makes it a potent nitrating agent in organic synthesis.