Question

Which of the following will not produce hydrogen gas?

• A. Electrolysis of mildly acidified water
• B. Electrolysis of NaCl in Nelson's cell
• C. Reaction of Zn with concentrated H₂SO₄
• D. Reaction of Zn with NaOH

Answer 1

The correct option is C

Reaction of Zn with concentrated H₂SO₄

Water on electrolysis decomposes into ${\text{H}}_2$ and ${\text{O}}_2$ gases.
In Nelson's cell, aqueous $\text{NaCl}$ is electrolyzed to give hydrogen and chlorine gas.

$\text{Zn}$ reacting with $\text{NaOH}$ liberates ${\text{H}}_2$ gas.

$\text{Zn + 2NaOH}\to {\text{Na}}_2{\text{ZnO}}_2{\text{+ H}}_2$

But when $\text{Zn}$ reacts with concentrated ${\text{H}}_2{\text{SO}}_4$,

${\text{Zn + 2H}}_2{\text{SO}}_4\text{(conc.)}\to {\text{ZnSO}}_4{\text{+ SO}}_2{\text{+ 2H}}_2\text{O}$