What are the compounds formed when white phosphorus is dissolved in boiling $NaOH$ solution in an inert atmosphere?

Mercury $(II)$ chloride solution on reaction with gaseous ammonia forms:

Ionic radius (in $\mathring{A}$) of $As^{3+}$,$Sb^{3+}$ and $Bi^{3+}$ follow the order:

Which of the following halides does not exist?

$HNO_3 + P_4O_{10} \to 4HPO_3 + X$. $X$ is

On heating,lead$(II)$ nitrate gives a brown gas $(A).$ The gas $(A)$ on cooling changes to a colourless solid/liquid $(B).$ $(B)$ on heating with $NO$ changes to a blue solid $(C).$ The oxidation number of nitrogen in solid $(C)$ is :