Which of the following gases is diamagnetic and neutral towards water?

$N_2$ combines with metals to form:

Which of the following forms of phosphorus is thermodynamically the most stable?

Choose the correct statement$(s)$ among the following.
$A$. $SnCl_2 \cdot 2 H_2O$ is a reducing agent.
$B$. $SnO_2$ reacts with $KOH$ to form $K_2[Sn(OH)_6]$.
$C$. $A$ solution of $PbCl_2$ in $HCl$ contains $Pb^{2+}$ and $Cl^{-}$ ions.
$D$. The reaction of $Pb_3O_4$ with hot dilute nitric acid to give $PbO_2$ is a redox reaction.

When $NH_3$ is passed over heated $CuO$,it gets oxidized to form .................. .

Which among the following is non-poisonous in nature?