Identify the reaction which does not liberate hydrogen?

The reaction that does not liberate hydrogen is allowing a solution of sodium in liquid ammonia to stand. Sodium dissolves in liquid ammonia to form a deep blue solution containing solvated electrons and sodium amide (NaNH2). The solvated electrons are responsible for the blue color and strong reducing power. Hydrogen gas is not directly liberated in this process. The other reactions listed produce hydrogen gas:

• Reaction of lithium hydride with B2H6: This reaction produces diborane(B2H6) and hydrogen gas (H2).
• Reaction of zinc with aqueous alkali: Zinc reacts with aqueous alkali (like NaOH) to produce hydrogen gas.
• Electrolysis of acidified water using Pt electrodes: Electrolysis of water splits it into hydrogen and oxygen gases at the cathode and anode, respectively.