Which element from group $15$ ($V$ group) forms the most basic compound with hydrogen?

The reddish-brown coloured gas formed when nitric oxide is oxidised by air is

Which among the following group $15$ elements does not exhibit allotropy?

$NH_3$ reacts with bleaching powder to give:

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.

Identify the correct set of $13^{th}$ group elements which do not form amphoteric oxides?