Orthophosphorus acid on disproportionation gives $PH_3$ and another oxoacid of phosphorus '$X$'. The basicity of $X$ is

On heating ammonium dichromate,the gas evolved is

Nitric acid forms an oxide of nitrogen on reaction with $P_{4}O_{10}$. Write the reaction involved. Also,write the resonating structures of the oxide of nitrogen formed.

How many bridging oxygen atoms are present in $P_4O_{10}$?

Amongst the following compounds:
$I.$ $H_5P_3O_{10}$
$II.$ $H_6P_4O_{13}$
$III.$ $H_5P_5O_{15}$
$IV.$ $H_7P_5O_{16}$
Which of these are non-cyclic phosphates?

Which of the following elements forms a new compound when exposed to air?