Which of the following hydrogen halides reacts with AgNO₃(aq.) to give a precipitate that dissolves in Na₂S₂O₃ (aq.) ?

In the reaction

$$\mathrm{2X+B_2H_6\to[BH_2(X)_2]^+[BH_4]^-}$$

the amine(s) X is(are) :

The nitrogen oxide(s) that contain(s) N-N bond(s) is(are)

A solution of colourless salt H on boiling with excess NaOH produces a non-flammable gas. The gas evolution ceases after sometime. Upon addition of Zn dust to the same solution, the gas evolution restarts. The colourless salt(s) H is(are):