In which of the following ranges can nitrogen exhibit various oxidation states?

Given below are two statements:
Statement $I$: The halogen that makes the longest bond with hydrogen in $HX$ has the smallest covalent radius in its group.
Statement $II$: $A$ group $15$ element's hydride $EH_3$ has the lowest boiling point among corresponding hydrides of other group $15$ elements. The maximum covalency of that element $E$ is $4$.
In the light of the above statements, choose the correct answer from the options given below.

Which of the following oxides of nitrogen is coloured?

Nitrogen is liberated by the thermal decomposition of only:

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.

With which of the following does $FeSO_4$ form a brown ring?