What happens when iron is treated with concentrated nitric acid $(HNO_3)$?

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

In the $15^{th}$ group of the periodic table,the elements $N, P, As, Sb$,and $Bi$ are present. As we move from $N$ to $Bi$,how do the oxides with the general formula change?

What happens when $H_{3}PO_{3}$ is heated?

Discuss the variations in atomic and ionic radii of elements,the trends in ionisation enthalpies and electronegativity of group-$15$ elements.

Extra pure $N_2$ can be obtained by heating :-