Which of the following fluorides does not exist?

Identify the reactions in which $N_2$ is liberated.
$a. \ (NH_4)_2SO_4 + NaOH \longrightarrow$
$b. \ NH_3 + Cl_2 \longrightarrow$ (excess $Cl_2$ is not specified, but $N_2$ is formed when $NH_3$ is in excess)
$c. \ (NH_4)_2Cr_2O_7 \xrightarrow{\Delta}$
$d. \ NH_4NO_3 \xrightarrow{\Delta}$
$e. \ NH_4Cl_{(aq)} + NaNO_{2_{(aq)}} \longrightarrow$

When $PbO_2$ reacts with conc. $HNO_3$,the gas evolved is:

Which of the following matches is correct?

What is the product formed when ammonia reacts with excess chlorine?

Nitric acid is an oxidising agent and reacts with $PbO$ but it does not react with $PbO_{2}$. Explain why?