$P_2O_5$ is heated with water to give:

In $P_4O_6$,how many oxygen atoms are attached to each phosphorus atom?

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:

Why does $NO_2$ dimerise?

Which of the following combines with $Fe(II)$ ions to form a brown complex?

$Cu +$ conc. $HNO_3$ (hot) $\rightarrow Cu(NO_3)_2 + X$ (oxide of nitrogen);
then $X$ is