Question

I. Gas X is liberated at the anode during the electrolysis of molten NaCl.​

II. Gas Y is liberated at the cathode during the electrolysis of NaCl solution.​

Identify gases X and Y.

• A. X: $O_2$ ; Y: $H_2$
• B. X: ${Cl}_2$ ; Y: $H_2$
• C. X: $H_2$ ; Y: ${Cl}_2$
• D. X: $H_2$ ; Y: $O_2$

Answer 1

The correct option is B X: ${Cl}_2$ ; Y: $H_2$

When molten NaCl is electrolysed, only ${Na}^{+}$ and ${Cl}^{-}$ ions are present. At the anode, two chlorine ions lose their electrons to liberate chlorine gas.
So, molten NaCl will produce chlorine gas at the anode.

The chemical reaction occuring at the anode is:
${2Cl}^{-}$(aq.) $\to$ ${Cl}_2$(g) + ${2e}^{-}$

So X is ${Cl}_2$.

On the other hand, when NaCl solution is electrolysed, $H^{+}$ and ${OH}^{-}$ ions are also present with ${Na}^{+}$ and ${Cl}^{-}$ ions. At the cathode, $H^{+}$ ions are reduced and they liberate hydrogen gas.

The chemical reaction at the cathode is:
${2H}^{+}$(aq.) + ${2e}^{-}$ $\to$ $H_2$(g)

Hence, the NaCl solution will produce hydrogen gas at the cathode.

So Y is $H_2$.

The correct answer is option (d).