Which reaction$(s)$ among the following produce dinitrogen?
$1. NH_4Cl(aq) + NaNO_2(aq) \longrightarrow$
$2. NH_2CONH_2 + 2H_2O \longrightarrow$
$3. Ba(N_3)_2 \longrightarrow$
$4. NH_4Cl + Ca(OH)_2 \longrightarrow$

Which of the following is an amphoteric oxide?

How can you explain the higher stability of $BCl_3$ as compared to $TlCl_3$?

The atomic number of $N$ is $7$. The atomic number of the $3$rd member of the nitrogen family is:

Account for the following observations:
$(A)$ $AlCl_3$ is a Lewis acid.
$(B)$ Though fluorine is more electronegative than chlorine yet $BF_3$ is a weaker Lewis acid than $BCl_3$.
$(C)$ $PbO_2$ is a stronger oxidizing agent than $SnO_2$.
$(D)$ The $+1$ oxidation state of thallium is more stable than its $+3$ state.

What is the color of $PCl_5$?