What is the similarity between $NH_3$ and $PH_3$?

Which statement is incorrect for nitric oxide $(NO)$?

The stable bivalency of $Pb$ and trivalency of $Bi$ is

Find the correct statements related to group $15$ hydrides.
$A$. Reducing nature increases from $NH_3$ to $BiH_3$
$B$. Tendency to donate lone pair of electrons decreases from $NH_3$ to $BiH_3$
$C$. The stability of hydrides decreases from $NH_3$ to $BiH_3$
$D$. $HEH$ bond angle decreases from $NH_3$ to $SbH_3$ ($E$ = Elements of group $15$)
Choose the correct answer from the options given below:

$A$ hydride of nitrogen which is acidic is

The passivity of iron in concentrated nitric acid is due to