Phosphorus pentoxide $(P_4O_{10})$ is used as a ........ .

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

Pure nitrogen can be prepared from

Which of the following statements are correct?
$(I)$ $P_4$ molecule is very reactive because of angular strain.
$(II)$ The basicity of $H_3PO_3$ is $3$.
$(III)$ In gas phase,all $P-Cl$ bonds of $PCl_5$ have same bond length.
$(IV)$ In solid state,$PCl_5$ exists as an ionic solid,in which anion $[PCl_6]^-$ has octahedral and cation $[PCl_4]^+$ has tetrahedral shape.

The basic character of hydrides of the $V$-group elements decreases in the order:

$A$ hydride of nitrogen which is acidic is