Question

Identify the reaction which does not liberate hydrogen :

• A. Reaction of zinc with aqueous alkali.
• B. Electrolysis of acidified water using $Pt$ electrodes.
• C. Allowing a solution of sodium in liquid ammonia to stand.
• D. Reaction of lithium hydride with $B_2H_6$

Answer 1

The Correct Option is D

To identify the reaction that does not liberate hydrogen, we need to examine each of the given reactions and determine whether hydrogen gas is produced.

1. Reaction of zinc with aqueous alkali:
   When zinc reacts with aqueous alkali (such as sodium hydroxide), it forms sodium zincate and liberates hydrogen gas. The reaction is as follows: Zn + 2NaOH \rightarrow Na_2ZnO_2 + H_2 \uparrow. Thus, this reaction liberates hydrogen.
2. Electrolysis of acidified water using Pt electrodes:
   In the electrolysis of acidified water, hydrogen gas is produced at the cathode. The overall reaction is: 2H_2O \rightarrow 2H_2 + O_2. Thus, this reaction liberates hydrogen.
3. Allowing a solution of sodium in liquid ammonia to stand:
   Sodium dissolved in liquid ammonia forms a deep blue solution and slowly releases hydrogen gas upon standing due to the following reaction: 2Na + 2NH_3 \rightarrow 2NaNH_2 + H_2 \uparrow. Thus, this reaction liberates hydrogen.
4. Reaction of lithium hydride with B_2H_6:
   When lithium hydride reacts with diborane (B_2H_6), a compound such as lithium borohydride is formed, but no hydrogen gas is liberated. The reaction can be represented as: 2LiH + B_2H_6 \rightarrow 2LiBH_4. Therefore, hydrogen gas is not liberated in this reaction.

Based on the analysis above, the reaction of lithium hydride with B_2H_6 is the one that does not liberate hydrogen. Therefore, the correct answer is the Reaction of lithium hydride with B_2H_6.