In the electrolysis of which solution `OH^(-)` ions are discharged in preference to `Cl^(-)` ions?

In the electrolysis of which solution, OH^- ions are discharged in preference to CI^- ions:

If mercury is used as cathode in the electrolysis of NaCl solution, the ions discharged at cathode are

Do acidic solutions contain OH^(-) ions ?

In the electrolysis of a solution containing H^(+) and Cu^(2+) ions, at the cathode H^(+) ions are liberated in preference to Cu^(2+) ions. Is the statement correct ?

In the electrolysis of NaCI solution, for the manufacture of NaOH, the ion discharged at cathode is H^(o+) .

In the electrolysis of NaCI solution, for the manufacture of NaOH, the ion discharged at cathode is H^(o+) .