Four half reactions I to IV are shown below: I. $2\mathrm{Cl^-}\rightarrow\mathrm{Cl_2}+2e^-$ II. $4\mathrm{OH^-}\rightarrow\mathrm{O_2}+2\mathrm{H_2O}+4e^-$ III. $\mathrm{Na^+}+e^-\rightarrow\mathrm{Na}$ IV. $2\mathrm{H^+}+2e^-\rightarrow\mathrm{H_2}$ Which two of these reactions are most likely to occur when concentrated brine is electrolysed?

CBSE Class 12 · 2023 · Redox Reactions and ElectrochemistryMultiple Choice

Four half reactions I to IV are shown below:
I.

2 C l^{-} \to C l_{2} + 2 e^{-}

II.

4 O H^{-} \to O_{2} + 2 H_{2} O + 4 e^{-}

III.

N a^{+} + e^{-} \to Na

IV.

2 H^{+} + 2 e^{-} \to H_{2}

Which two of these reactions are most likely to occur when concentrated brine is electrolysed?

Answer: (B)

In concentrated brine, Cl

^{-}

is oxidised at the anode (Cl

_{2}

evolved, favoured by overvoltage of O

_{2}

), and at the cathode water/H

^{+}

is reduced to H

_{2}

— Na

^{+}

is not reduced in aqueous solution.
Hence reactions I and IV occur.

CBSE Class 12 Board · 2023 · Single correct option