Which element does not show allotropy:

Which of the following oxyacids does not contain a $P-O-P$ bond?

Which of the following produces $NO_2$ gas on heating?

Pure $HNO_3$ is colorless. However,it turns slightly brown when exposed to light due to its decomposition into $.....$.

Small quantities of $NO$ and $HNO_3$ are formed as impurities when $N_2$ is prepared from $NH_4Cl_{(aq)}$ and $NaNO_{2(aq)}$. These impurities can be removed by passing the $N_2$ gas through which of the following?

Phosphorus on reaction with sulphuryl chloride gives a compound $X$, which on complete hydrolysis gives $Y$. $X$ and $Y$ are respectively