Which of the following is a true acidic anhydride?

Which of the following is obtained by catalytic oxidation of ammonia?

Which of the following statements is true for $PH_3$?

The structural formula of hypophosphorus acid is

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 one of the following is not correct?