Which of the following is a true acidic anhydride?

The reaction of zinc with dilute and concentrated nitric acid,respectively,produces:

Heating $(NH_4)_2Cr_2O_7$ liberates a gas. The same gas is obtained by:

Sodium nitrite is reacted with $H_2SO_4$ to form $NaHSO_4$,$HNO_3$,water and $X$. Gold is dissolved in aqua regia to form water,$AuCl_4^{-}$ and $Y$. $X$ and $Y$ are respectively

Among the following compounds,the one which does not produce nitrogen gas upon heating is

Nitrogen dioxide is dissolved in water to produce