What is the correct order of acidic character for the given oxides?

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.

Nitrous oxide $(N_2O)$:

The reaction of $P_4$ with $X$ leads selectively to $P_4O_6$. The $X$ is

Nitrogen exists as a diatomic molecule $(N_2)$ and phosphorus as $P_4$. Why?

How many isotopes of nitrogen gas are stable? Which are they?