Which nitrogen trihalide is the least basic?

Which of the following dissolves in hot conc. $NaOH$ solution?

The number of $P-O-P$ bonds in cyclic metaphosphoric acid is

Nitric acid oxidises phosphorus to

Which element does not form complexes?

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: