Which of the following oxides of nitrogen is a mixed anhydride of two acids?

Nitrogen forms only $NCl_3$,whereas phosphorus forms both $PCl_3$ and $PCl_5$. Why?

White phosphorus is heated with concentrated $NaOH$ in $CO_2$ atmosphere to form a gas $A$ and compound $B$. When $A$ is bubbled into aqueous $CuSO_4$ solution,copper phosphide and $C$ are formed. $B$ and $C$ are respectively:

State the oxoacids of phosphorus with their formula,methods of preparation,and the presence of characteristic bonds in their structure.

In an Ostwald process:
$NH_3 + O_2 \xrightarrow[Pt]{\Delta} x + H_2O$
$x + O_2 \to y$
$y + H_2O (excess) \to x + z$
The incorrect option is:

$P_4 + 3NaOH + 3H_2O \to A + 3NaH_2PO_2$. Here,$A$ is: