Which one of the following elements occurs free in nature?

Cyanogen gas is obtained in the reaction:

Which of the following combines with $Fe(II)$ ions to form a brown complex?

Name three oxoacids of nitrogen. Write the disproportionation reaction of that oxoacid of nitrogen in which nitrogen is in $(+3)$ oxidation state.

The structure of white phosphorus is ........ .

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?