Which substance is used as a smoke screen in warfare?

Assertion $:$ Reducing nature of pnicogen hydrides increases on moving down the group.
Reason $:$ Thermal stability of pnicogen hydrides decreases on moving down the group.

The bond energies (in $kJ \ mol^{-1}$) of $N-H$,$P-H$,and $As-H$ are respectively:

The number of $P-OH$ bonds and the oxidation state of the phosphorus atom in pyrophosphoric acid $(H_4P_2O_7)$ respectively are

Which of the following substances is a deliquescent ionic solid?

The gases liberated when zinc reacts with dilute and conc. $HNO_3$ respectively are