In which oxidation state,group $15$ elements act as Lewis base?

During which of the following processes is phosphine $(PH_3)$ $NOT$ obtained?

Though nitrogen exhibits $+5$ oxidation state,it does not form pentahalide. Give reason.

Write a note on allotropes of phosphorus.

$P_2O_3 + H_2O \rightarrow X$
$Red \ P_4 + \text{alkali} \rightarrow Y$
$X$ and $Y$ are oxoacids of phosphorus. The number of $P-OH$ bonds in $X$ and $Y$ respectively is:

Phosphine is obtained from the following compound: