The number of $H$ atoms attached to the phosphorus atom in hypophosphorous acid is

$NH_3 + O_2 \xrightarrow[500 \ K]{Pt} A + H_2O$
$A + O_2 \to B$; $B + H_2O \to C + A$
$A, B$ and $C$ respectively are

Which of the following compounds does not give an oxyacid of the central atom on hydrolysis?

$A$ $p$-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 $E$.

Which of the following halides does not exist?

What is the correct order of acidic character for the following oxides: $SO_2, CO_2, CO, N_2O_5$?