The element that does $NOT$ exhibit allotropy is$-$

$A$ nitrogen oxide that forms "in situ" when dilute $FeSO_4$ is treated with an aqueous solution of nitrate ion and then carefully adding conc. $H_2SO_4$ along the sides of the test tube, is

$H_4P_4O_{12}$ and $H_3P_3O_9$ have the same:

When $KNO_3$ is heated with concentrated $H_2SO_4$,brown fumes are evolved. These fumes are due to:

White phosphorus reacts with thionyl chloride to give

Which of the following molecules has the highest number of $P-H$ bonds?