Question

On reaction with sodium, which of the following compounds liberate hydrogen gas?

• A. Ethane
• B. Propylene
• C. Acetylene
• D. Benzene

Answer 1

Answer: (C)

Only acetylene has acidic hydrogens and hence reacts with Na to evolve $H_2$ gas.
$2\text{HC}\equiv \text{CH}+2\text{Na}\to 2\text{HC}\equiv \text{CNa}+{\text{H}}_2$