Which of the following formulas represents laughing gas?

Give the preparation of ammonia. Discuss the physical and chemical properties of ammonia. Give the uses of ammonia.

In pyrophosphorous acid,the number of $P-OH$,$P-H$,and $P=O$ linkages are respectively:

Which element does not show allotropy:

Dilute nitric acid on reaction with $Ag$ liberates

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: