Statement I: Electrolysis of NaCl solution gives chlorine at anode instead of oxygen

Statement II: Formation of oxygen at anode requires over voltage

Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I

The correct answer is option 1. Both Statement I and Statement II are correct, and Statement II is the correct explanation of Statement I.

Statement I:  Electrolysis of NaCl solution gives chlorine at the anode instead of oxygen.
This statement is correct. During the electrolysis of sodium chloride \((NaCl)\) solution (brine), water molecules and chloride ions \((Cl^-)\) are present in the solution. At the anode (positive electrode), water molecules can undergo oxidation to produce oxygen gas \((O_2)\) according to the half-reaction:

\(2H_2O(l) \rightarrow  O_2(g) + 4H^+(aq) + 4e^-\)

However, chloride ions \((Cl^-)\) in the \(NaCl\) solution can also undergo oxidation at the anode to form chlorine gas \((Cl_2)\) according to the half-reaction:

\(2Cl^-(aq) \rightarrow Cl_2(g) + 2e^-\)

The oxidation of chloride ions to produce chlorine gas is more favorable than the oxidation of water to produce oxygen. As a result, chlorine gas evolved at the anode during the electrolysis of the NaCl solution.

Statement II: Formation of oxygen at the anode requires overvoltage.

This statement is also correct and provides the correct explanation for Statement I. Overvoltage is the extra potential or voltage that needs to be applied during electrolysis to drive a reaction at the electrode. In the case of the anode, the formation of oxygen from water (the half-reaction mentioned in Statement I) typically requires an overvoltage to occur.

The overvoltage is necessary because the natural tendency for the anode reaction is to preferentially oxidize chloride ions to form chlorine gas (as stated in Statement I). To drive the less favorable oxygen evolution reaction, additional voltage is needed to overcome the activation energy barrier for this reaction.

In summary, both statements are correct. Statement I correctly states that electrolysis of NaCl solution gives chlorine at the anode instead of oxygen. Statement II is the correct explanation for this phenomenon, stating that the formation of oxygen at the anode requires overvoltage due to the preference for chloride ion oxidation and the need to overcome the activation energy barrier for the oxygen evolution reaction.