Which allotropic form of phosphorus is the most stable,least reactive,and possesses a graphite-like structure?

The decrease in stability of the higher oxidation state in the $p-$block elements with an increasing atomic number is due to:

Which one of the following is correct with respect to basic character?

Which gas,when absorbed by ferrous sulfate,produces a dark brown color?

Which oxide is alkaline?

$A$ colourless,neutral,paramagnetic oxide of nitrogen '$P$' on oxidation gives reddish brown gas $Q$. $Q$ on cooling gives colourless gas $R$. $R$ on reaction with $P$ gives blue solid $S$. Identify $P, Q, R, S$ respectively.