Which of the following allotropes of phosphorus is the most stable?

At what temperature is white phosphorus heated to obtain red phosphorus (in $K$)?

Dinitrogen and dioxygen,the main constituents of air,do not react with each other in the atmosphere to form oxides of nitrogen because:

In the ring test of $NO_{3}^{-}$ ion,$Fe^{2+}$ ion reduces nitrate ion to nitric oxide,which combines with $Fe^{2+}_{(aq)}$ ion to form a brown complex. Write the reactions involved in the formation of the brown ring.

Which of the nitrogen oxides is obtained when ammonium nitrate is heated?

$Assertion :$ Nitrogen and oxygen are the main components in the atmosphere but these do not react to form oxides of nitrogen.
$Reason :$ The reaction between nitrogen and oxygen requires high temperature.