The number of $H$ atoms attached to the phosphorus atom in hypophosphorous acid is

What is produced when $Ag$ is heated with concentrated $HNO_3$?

Which gas,when absorbed by ferrous sulfate,produces a dark brown color?

Which one of the following compounds on strong heating evolves ammonia gas?

White phosphorus is heated with concentrated $NaOH$ in $CO_2$ atmosphere to form a gas $A$ and compound $B$. When $A$ is bubbled into aqueous $CuSO_4$ solution,copper phosphide and $C$ are formed. $B$ and $C$ are respectively:

Which of the following halides is most acidic?