Which reaction does not produce ammonia?

On heating lead $(II)$ nitrate gives a brown gas $'A'$. The gas $'A'$ on cooling changes to a colourless solid $'B'$. Solid $'B'$ on heating with $NO$ changes to a blue solid $'C'$. Identify $'A'$,$'B'$ and $'C'$,write the reactions involved,and draw the structures of $'B'$ and $'C'$.

$A$ nitrogen oxide that forms "in situ" when dilute $FeSO_4$ is treated with an aqueous solution of nitrate ion and then carefully adding conc. $H_2SO_4$ along the sides of the test tube, is

For the properties mentioned,the correct trend for the different species is in

$FeSO_4$ gives a brown ring with ........

The element which forms oxides in all oxidation states from $+I$ to $+V$ is