Which of the following oxoacids of phosphorus has the strongest reducing property?

Dinitrogen and dioxygen are main constituents of air but these do not react with each other to form oxides of nitrogen because .......................

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

The following are some statements related to $VA$ group hydrides:
$I$. Reducing property increases from $NH_3$ to $BiH_3$.
$II$. Tendency to donate lone pair decreases from $NH_3$ to $BiH_3$.
$III$. Thermal stability of hydrides decreases from $NH_3$ to $BiH_3$.
$IV$. Bond angle of hydrides decreases from $NH_3$ to $BiH_3$.
The correct statements are:

Which one of the following is correct with respect to basic character?

Assertion : Although $PF_5, PCl_5$ and $PBr_5$ are known,the pentahalides of nitrogen have not been observed.
Reason : Phosphorus has lower electronegativity than nitrogen.