Aqueous \(NaCl\) solution is electrolyzed. The product formed at the anode is:

\(Cl_2\) gas

The correct answer is option 4. \(Cl_2\) gas.

When an aqueous NaCl solution is electrolyzed, the product formed at the anode is \(Cl_2\) gas.

Here's why:

During electrolysis, an applied voltage forces the dissociation of \(NaCl\) molecules in the solution into \(Na^+\) and \(Cl^-\) ions.

These ions migrate towards their respective electrodes: \(Na^+\) ions move towards the cathode (negative electrode), and \(Cl^-\) ions move towards the anode (positive electrode).

At the cathode, water molecules \((H_2O)\) present in the solution are attracted and reduced to hydrogen gas \((H_2)\), according to the reaction:

\(2H_2O + 2e^- \longrightarrow H_2 + 2OH^-\)

At the anode, chloride ions \((Cl^-)\) lose electrons and are oxidized to chlorine gas \((Cl_2)\), according to the reaction:

\(2Cl^- \longrightarrow Cl_2 + 2e^-\)

Therefore, in an aqueous \(NaCl\) solution electrolysis, chlorine gas is produced at the anode, not hydrogen gas.