$HNO_3 + P_4O_{10} \to 4HPO_3 + X$. $X$ is

Which of the following oxides is most acidic?

The products of hydrolysis of isohypophosphoric acid are the same as those of which of the following compounds?

Regarding the hydrides of group $15$ elements $EH_{3}$ $(E = N, P, As, Sb, Bi)$, select the correct statement from the following:
$A$. The stability of hydrides decreases down the group.
$B$. The basicity of hydrides decreases down the group.
$C$. The reducing character increases down the group.
$D$. The boiling point increases down the group.
Choose the correct answer from the options given below:

Which of the following is the correct decreasing order of bond angles in the hydrides of group $15$ elements?

$H_4P_4O_{12}$ and $H_3P_3O_9$ have the same: