$N_2O_3$ is a/an.......

Which element does not show allotropy:

Which one of the following contains a $P-O-P$ bond?

Zinc on reaction with concentrated nitric acid gives an oxide of nitrogen $(A)$. Zinc with dilute nitric acid gives another oxide of nitrogen $(B)$. Oxidation numbers of nitrogen in $(A)$ and $(B)$ are respectively:

What is the maximum concentration of aqueous $HNO_3$ that can be obtained by distillation with concentrated $H_2SO_4$ in terms of percentage by mass (in $\%$)?

The reaction that does not produce nitrogen is