The product, which is not obtained during the electrolysis of brine solution is

Strategy: The electrolysis of brine (concentrated aqueous $\ce{NaCl}$) involves competing reactions at the electrodes. Analyze the discharge potential of available ions to determine the net products in the solution.

Step 1: Analyze electrode reactions

• At Cathode: Preferen\ce is given to the reduction of water over $\ce{Na^+}$ because $E°_{\ce{H2O/H2}}$ is higher. $\ce{2H2O + 2e^- \rightarrow H2(g) + 2OH^-(aq)}$ Product: Hydrogen gas.

• At Anode: Due to overvoltage, $\ce{Cl^-}$ is oxidised in preferen\ce to water. $\ce{2Cl^- \rightarrow Cl2(g) + 2e^-}$ Product: Chlorine gas.

Step 2: Determine solution components The remaining $\ce{Na^+}$ ions and the newly formed $\ce{OH^-}$ ions combine in the solution to form NaOH.

Step 3: Identify the missing product Comparing with the options, $\ce{HCl}$ is not a direct product of the electrolysis pro\cess.

$\boxed{\text{Answer: (b) HCl}}$