Which of the following nitrogen trihalides is the most basic?

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.

The decreasing order of the number of ionisable hydrogen atoms in the following molecules is:
$I$. $H_3PO_4$
$II$. $H_3PO_3$
$III$. $H_3PO_2$
$IV$. $H_4P_2O_6$

Which gas is formed in the atmosphere due to lightning?

$Fe$ is made passive by

The minimum temperature required for a non-catalytic reaction between $N_2$ and $O_2$ is (in $K$)