Question

In which of the following reactions, dihydrogen is not evolved?

• A. Oxidation of sodium borohydride with iodine
• B. Hydrolysis of boranes
• C. Heating the adduct formed by the reaction of ammonia with diborane
• D. Burning of diborane in oxygen

Hint:

Combustion reactions typically convert hydrogen into water rather than releasing it as \( H_2 \) gas.

Answer 1

The Correct Option is D

Step 1: Understanding the given reactions - Sodium borohydride (\( NaBH_4 \)) reacts with iodine to release \( H_2 \): \[ NaBH_4 + I_2 \rightarrow NaI + B_2H_6 + H_2 \] - Hydrolysis of boranes also releases \( H_2 \): \[ B_2H_6 + H_2O \rightarrow B(OH)_3 + H_2 \] - The reaction of ammonia with diborane forms an adduct and releases \( H_2 \): \[ B_2H_6 + NH_3 \rightarrow (BH_3)_2 \cdot NH_3 + H_2 \] - However, burning diborane in oxygen results in complete combustion, forming \( B_2O_3 \) and water vapor, without producing dihydrogen: \[ B_2H_6 + O_2 \rightarrow B_2O_3 + H_2O \]