Which of the following compounds does not give dinitrogen on heating?

Pure $N_2$ gas is obtained from

Which of the following oxides of nitrogen is a coloured gas?

Which of the following nitrogen trihalides is the most basic?

By the action of hot conc. $H_2SO_4,$ phosphorus changes to

Account for the following observations:
$(A)$ $AlCl_3$ is a Lewis acid.
$(B)$ Though fluorine is more electronegative than chlorine yet $BF_3$ is a weaker Lewis acid than $BCl_3$.
$(C)$ $PbO_2$ is a stronger oxidizing agent than $SnO_2$.
$(D)$ The $+1$ oxidation state of thallium is more stable than its $+3$ state.