Electrolysis of concentrated aqueous NaCl prioritizes water reduction at cathode over Na+.

Steps:

• Identify ions present: Na+(aq), Cl-(aq), H2O (which provides H+(aq)/OH-(aq)).
• At cathode (reduction): H2O reduces to H2(g) + OH-(aq) because its potential (-0.83 V) is less negative than Na+ (-2.71 V).
• At anode (oxidation): Cl-(aq) oxidizes to Cl2(g) due to high concentration overcoming OH- preference (overpotential for O2 evolution).
• Overall: H2 and Cl2 produced; OH- accumulation raises pH.

Why B is correct:

• pH increases as OH-(aq) forms at cathode via 2H2O + 2e- → H2 + 2OH-, per standard electrode potentials.

Why the others are wrong:

• A: pH rise is from cathode OH-, not anode where Cl- oxidizes preferentially over OH-.
• C: No solid Na produced; cathode reduces water to H2, not Na+.
• D: Products differ—aqueous gives H2/OH- and Cl2; molten gives Na and Cl2.

Final answer: B