$\begin{array}{1 1} \text{(1) Reaction of zinc with aqueous alkali.} \\ \text{(2) Electrolysis of acidified water using Pt electrodes.} \\ \text{(3) Allowing a solution of sodium in liquid ammonia to stand.} \\ \text{(4) Reaction of lithium hydride with $B_2H_6$} \end{array} $
