Electrolysis products of concentrated aqueous NaCl Steps:

• Ions present: Na+, Cl-, and H2O (providing H+ and OH-).
• At cathode: Water reduces to H2 and OH- (E° = -0.83 V), not Na+ (E° = -2.71 V), so Na+ remains.
• At anode: Concentrated Cl- oxidizes to Cl2 (overdischarge of OH- to O2).
• Overall: Cl- depletes as Cl2, Na+ pairs with OH- to form NaOH, decreasing NaCl concentration.

Why B is correct:

• Concentration decreases because Na+ is not discharged (water reduces preferentially, per standard electrode potentials), leaving Na+ while Cl- is removed as Cl2.

Why the others are wrong:

• A: pH increases from OH- production at cathode, not OH- losing electrons (which would be oxidation at anode).
• C: No sodium discharged (Na+ not reduced in water); water, not H+, is discharged at cathode.
• D: Molten NaCl yields Na and Cl2; aqueous yields H2, Cl2, NaOH due to water's involvement.

Final answer: B