Which oxides of nitrogen are present in significant amounts in the atmosphere?

$A$ $p$-block element $(E)$ and hydrogen form a binary cation $(EH_{x}^{+})$, while $EH_{3}$ on treatment with $K_{2}HgI_{4}$ in alkaline medium gives a precipitate of basic mercury$(II)$amido-iodine. Given below are first ionisation enthalpy values $(kJ \ mol^{-1})$ for the first element of each group $13, 14, 15$, and $16$. Identify the correct first ionisation enthalpy value for element $E$.

Identify the incorrect statement from the following:

$NH_3 + O_2 \xrightarrow[\Delta]{Pt} A + H_2O$ ;
$A + O_2 \to B$ ;
$B + O_2 + H_2O \to C$
$A, B$ and $C$ are:

When orthophosphoric acid is heated to $600\,^oC$,it forms .................. .

Total number of acidic oxides among $N_2O_3, NO_2, N_2O, Cl_2O_7, SO_2, CO, CaO, Na_2O$ and $NO$ is $...........$