What are the number of $P - O - P$ bridges in phosphorus pentoxide $(P_4O_{10})$ and phosphorus trioxide $(P_4O_6)$ respectively?

$PbF_4$ and $PbCl_4$ exist,while $PbBr_4$ and $PbI_4$ do not exist. This is due to:

What is the active species in Nessler's reagent used for the identification of ammonia?

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 compounds does not produce ammonia upon heating?

Which compound is used in smoke screens?