Which of the following oxides of nitrogen is the mixed anhydride of nitrous acid and nitric acid?

The oxide of nitrogen that is the mixed anhydride of nitrous acid and nitric acid is Nitrogen pentoxide (N2O5).

Here's the step-by-step explanation:

1. Anhydrides are compounds that form acids when reacted with water. In this case, we are looking for an oxide of nitrogen that forms nitrous acid (HNO2) and nitric acid (HNO3) when reacted with water.

2. Nitrogen pentoxide (N2O5) is the one that fits this description. When N2O5 is reacted with water, it forms both nitrous acid and nitric acid.

3. The reaction is as follows: N2O5 + H2O -> HNO2 + HNO3

So, Nitrogen pentoxide (N2O5) is the mixed anhydride of nitrous acid and nitric acid.