‘Lapis-Lazuli’ is a blue-coloured precious stone. It is a mineral of the class:

Nitrogen dioxide cannot be prepared by heating:

$P_4O_{10}$ reacts with $HNO_3$ to give:

$A$ 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.

Which gas is used to provide an inert atmosphere?

What is the $P-P-P$ bond angle in white phosphorus?